2007 Little Goose Creek Fire provided by Mr. Steve Small, … · 2015. 5. 26. · 2007 Little Goose...

Cover Photos Provided By:

2007 Little Goose Creek Fire provided by Mr. Steve Small, Sheridan County Local Emergency

Planning Committee (LEPC) Chairman

2009 Ice Jam in the City of Sheridan provided by the City of Sheridan

June 2011 Connor Battle Field flood event provided by the Town of Ranchester

Table of Contents 1.0 Introduction ............................................................................................................................1

2.0 Mitigation Strategy .................................................................................................................2

Purpose of the Sheridan County Multi-Hazard Mitigation Plan ........................................................2

Authority .......................................................................................................................................2

Goals .............................................................................................................................................5

3.0 Funding ..................................................................................................................................5

4.0 Planning Process .....................................................................................................................6

Table 1: Core Planning Team Stakeholders .................................................................................7

Table 2: Flood Planning Team Stakeholders ................................................................................9

Table 3: Wildland Fire Planning Team Stakeholders ....................................................................9

5.0 Community Profile ................................................................................................................ 10

Figure 1: Overview map of Sheridan County and Participating Jurisdictions in the 2013 Sheridan

County Multi-Hazard Mitigation Plan ........................................................................................ 11

Table 2: Population Distribution and Growth Rate 1990-2012 ................................................... 11

Figure 2: Population Growth Charts for Sheridan County, City of Sheridan, Town of Ranchester,

Town of Dayton, and Town of Clearmont .................................................................................. 12

6.0 Development Trends in Sheridan County ............................................................................... 14

7.0 Community Capability Assessment ........................................................................................ 14

Table 3: Sheridan County Community Capabilities .................................................................... 15

8.0 Plan Implementation, Integration and Maintenance Procedures ............................................ 16

Implementation ........................................................................................................................... 16

Integration ................................................................................................................................... 16

Maintenance ................................................................................................................................ 18

Table 4: Sheridan County Multi-Hazard Mitigation Plan Monitoring Worksheet ......................... 19

Table 5: Suggested Schedule for Updating the Sheridan County Multi-Hazard Mitigation Plan ... 19

9.0 Public Participation ............................................................................................................... 20

10.0 Hazard Identification ............................................................................................................. 21

11.0 Hazards Risk Analysis ............................................................................................................ 22

Table 6: Current Hazard Summary Table ................................................................................... 23

Dam Failure ................................................................................................................................. 24

Figure 1: Location and Hazard Ranking of Dams in Sheridan County .......................................... 25

Figure 2: Dams currently inspected by the Wyoming State Engineers Office, Dam Safety Program

................................................................................................................................................ 27

Drought ....................................................................................................................................... 29

Figure 1: Drought Category by Week, Years 2000-2013 .............................................................. 31

Figure 2: Palmer Drought Severity Index (PDSI) 1895-2010 ........................................................ 32

Figure 3: Surface Water Supply Index (SWSI) June 2013 ............................................................ 33

Table 1: Value of Crop and Livestock Production for the State of Wyoming ............................... 35

Table 2: Production by Commodity for the State of Wyoming ................................................... 36

Drought Links ........................................................................................................................... 37

Earthquake .................................................................................................................................. 38

Figure 1: Historic Earthquakes in Wyoming ............................................................................... 39

Table 1: Abridged Modified Mercalli Intensity Scale ................................................................... 43

Table 2: Modified Mercalli Intensity Scale value and description ............................................... 44

Figure 2: 500-year probabilistic acceleration map (10% probability of exceedance in 50 years) .. 45

Figure 3: 1,000-year probabilistic acceleration map (5% probability of exceedance in 50 years) . 46

Figure 4: 2,500-year probabilistic acceleration map (2% probability of exceedance in 50 years) . 47

Table 2: HAZUS Probabilistic Scenario for Sheridan County ....................................................... 49

Table 3: County Impacts Rated by Loss Ratio ............................................................................ 50

Table 4: County Impacts Rated by Dollar Loss ........................................................................... 51

Flood and Ice Jamming ................................................................................................................. 53

Table 1: NFIP Community Status Book Results as of September 2013 ........................................ 55

Table 2: NFIP Loss Statistics January 1, 1978 through June 30, 2013 ........................................... 56

Figure 1: Sheridan County NFIP Policies and Claims and Public Assistance Projects .................... 57

Table 3: Sheridan County Flood History Data 1923-2012 ........................................................... 59

Figure 2: Sheridan County Flood Map Area ............................................................................... 68

Table 4: Critical Facilities and Parcel Changes from the Effective paper FIRMs for participating

NFIP communities to the 2012 DFIRMs ...................................................................................... 69

Table 5: Updated Flood Hazard Zone Designations for Sheridan County and Incorporated

Communities ............................................................................................................................ 69

Figure 4: Central Sheridan County Changes Since Last FIRM ...................................................... 70

Table 6: Number of Parcels Intersecting FIRM Floodplains by Jurisdiction .................................. 71

Table 7: Sheridan County Hazus‐MH Loss Estimates .................................................................. 71

Figure 5: City of Sheridan Parcels Intersecting FIRM Floodplains ................................................ 72

Figure 6: Town of Dayton Parcels Intersecting FIRM Floodplains ............................................... 73

Figure 7: Town of Ranchester Parcels Intersecting FIRM Floodplains ......................................... 74

Figure 8: Town of Clearmont Parcels Intersecting FIRM Floodplains .......................................... 75

Ice Jamming Overview .................................................................................................................. 76

Table 8: Reported Ice Jams for Sheridan County 1922-1971 ....................................................... 78

Table 9: Sheridan County Early Flood Warning System Stations ................................................. 80

Figure 9: Map of Sheridan County Early Flood Warning System Stations .................................... 81

Hail .............................................................................................................................................. 85

Table 1: Sheridan County Hail Event History 1937-2013............................................................. 82

Hazardous Materials .................................................................................................................... 95

Table 1: U.S. Department of Transportation Classes of Hazardous Materials and Sub-Classes .... 96

Table 2: Risk Management Plan (RMP) Facilities in Sheridan County.......................................... 99

Landslides .................................................................................................................................. 100

Figure 1: State of Wyoming Mapped Landslide Areas .............................................................. 100

Figure 2: Mapped Landslides in Sheridan County ..................................................................... 101

Figure 3: State of Wyoming Landslide Classifications ............................................................... 102

Table 3: Location of landslides in specific quadrangles: ........................................................... 103

Figure 4: Landslide Exposure Values ....................................................................................... 109

Figure 5: Building Exposure Values in Sheridan County............................................................ 110

Table 4: Building Exposure Values for Landslides for Sheridan County ..................................... 110

Lightning .................................................................................................................................... 112

Table 1: Recorded lightning events 1968-1994, Sheridan County ............................................. 113

Figure 1: Average annual lightning flash density for 1998-2000 over Wyoming. Each pixel

represents 5 km2. Illustration courtesy of Vaisala Inc. .............................................................. 116

Man-Made Hazards .................................................................................................................... 118

Mine Subsidence ........................................................................................................................ 120

Figure 1: Mined-out areas and mine subsidence in Wyoming. Gray areas represent mined-out

areas with subsidence. Solid areas represent mined-out areas with no known subsidence. ...... 121

Figure 2: Mined-out areas and subsidence near Sheridan ....................................................... 122




Table 1: Detail on the Subsidence Problems in Sheridan County .............................................. 126

Table 2: Underground Coal Mines in Sheridan County ............................................................. 126

Table 3: Underground Hard Rock Mines .................................................................................. 128

Tornado ..................................................................................................................................... 135

Table 1: Fujita Scale of Tornado Intensity ............................................................................... 135

Table 2: Reported tornadoes including those with associated damage in Sheridan County ....... 137

Figure 1: Statewide map of reported tornadoes by county and F-Scale Damage ....................... 138

Table 3: Sheridan County Damaging Tornado Events ............................................................... 139

Figure 2: Tornado Damage by County in 2004 USD (1907 - 2003) ............................................. 141

Table 5: Tornado Events by County (1907 - 2006) .................................................................... 142

Wildland Fire.............................................................................................................................. 144

Table 1: Sheridan County Fire Summary Table 2005-2010 ....................................................... 147

Table 2: Large Scale Wildland Fire Events in 2012 .................................................................... 148

Table 3: Sheridan County Wildfire Event History 1988-2007 .................................................... 149

Figure 1: News Article from November 2003 about dangerous wildland fire that caused the

evacuation of several homes in the Town of Dayton. ............................................................... 153

Figure 2: Fuel Typing for Years 2004-2005 ................................................................................ 156

Figure 3: Sheridan County Wildland Urban Interface Hazard Assessment Risk, Hazard, and Value

(RVH) Map .............................................................................................................................. 158

Figure 4: Building Exposure HAZUS Map ................................................................................. 159

Table 4: Wildland Urban Interface (Square Miles) ................................................................... 160

Figure 5: Wildland Urban Interface Comparison of Areas with and without Homes .................. 161

Figure 6: Sheridan County’s Overall Ranking when compared to 11 other Western Stated for

Existing and Potential WUI Risk. .............................................................................................. 162

Figure 7: Sheridan County’s State Ranking for Existing and Potential Wildland Fire Risk ........... 162

Table 5: Wildland-Urban Interface (Square Miles) ................................................................... 163

Figure 8: Number of Homes Built Inside the Wildland Urban Interface in Sheridan County in

comparison to 11 other Western States .................................................................................. 164

Figure 9: Sheridan County Wildland Urban Interface Areas With and Without Homes .............. 164

Table 6: Sheridan County, WY - West-Wide and State-Wide County Rankings .......................... 165

Figure 10: Second Homes Built in the Wildland Urban Interface .............................................. 165

Figure 11: Sheridan County Fire District Map .......................................................................... 167

Table 7: Sheridan County Fire Districts specific Hazard Areas, Risk, and Mitigation Actions ...... 168

Figure 12: Wildland Fire Mitigation Projects in the community of Story, WY ............................ 172

Table 8: American Recovery and Reinvestment Act Fuel Mitigation Projects in Sheridan County,

WY ......................................................................................................................................... 173

Figure 13: Before and After photos of Project Number 10-003................................................. 173




Winter Storm and Blizzards ........................................................................................................ 176

Table 1: Sheridan County Winter Storms 1886-2000 ................................................................ 178

12.0 Mitigation Strategy and Mitigation Actions ............................................................................. 200

Ranking Criteria.......................................................................................................................... 200

Table 1: Previous and Updated Hazard Mitigation Projects/Actions for Sheridan County, City of

Sheridan, Town of Clearmont, Town of Dayton, and Town of Ranchester ................................. 201

Table 2: Completed Hazard Mitigation Projects/Actions .......................................................... 212

Appendix Overview ........................................................................................................................ 217

Appendix A – Team Members ..................................................................................................... 218

Appendix B – Letters of Intent .................................................................................................... 221

Appendix C - Meeting Documentation and Worksheets ............................................................... 231

Appendix D – Public Outreach .................................................................................................... 281

Appendix E - Local, State, and Federal Grant Opportunities ......................................................... 293

Appendix F – Hazard Event Photos and Winter Storm Press Release ............................................ 295

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1.0 Introduction

Hazard mitigation is any action taken before, during, or after disaster to permanently eliminate or reduce the long-term risk to human life and property from natural and technological hazards. It is an essential element of emergency management, along with preparedness, response, and recovery. There is a cyclical relationship between the five phases of emergency management as defined by the Federal Emergency Management Agency’s (FEMA) National Preparedness Goal. The five areas which are currently defined as Mission Areas by FEMA are, Prevention, Protection, Mitigation, Response, and Recovery1. A community prepares for a disaster, and then responds when it occurs. Following the response, there is a transition into the recovery process, during which mitigation measures are evaluated and adopted. This, in turn, improves the preparedness posture of the community for the next incident, and so on. When successful, mitigation will lessen the impacts to such a degree that succeeding incidents will remain incidents and not become disasters. Hazard mitigation strives to reduce the impact of hazards on people and property through the identification of local natural and man-made hazards, the coordination of resources, programs, and authorities, and the identification and implementation of mitigation actions. The goal of such hazard mitigation measures is to prepare communities so they can make informed hazard mitigation efforts during community planning efforts pre and post disaster occurrences. One idea that was presented in the 2009 Sheridan County Multi-Hazard Mitigation plan and continues to be relevant is for this multi-hazard mitigation plan to assist communities identify natural and man-made hazard profiles and mitigation actions so post disaster efforts do not contribute to the increasing severity of the problem by allowing development or reconstruction to be completed in such a way as to simply restore damaged property as quickly as possible to pre-disaster conditions. Such efforts expedite a return to “normalcy”; however, replication of pre-disaster conditions results in a cycle of damage, reconstruction, and damage again. Hazard mitigation is needed to ensure that such cycles are broken, that post-disaster repairs and reconstruction take place after damages are analyzed, and that sounder, less vulnerable conditions are produced. Through a combination of regulatory, administrative, and engineering approaches, losses can be limited by reducing susceptibility to damage. Hazard mitigation provides the mechanism by which communities and individuals can break the cycle of damage, reconstruction, and damage again. Recognizing the importance of reducing community vulnerability to natural and technological hazards, Sheridan County is actively addressing the issue through the development and subsequent implementation of this plan. The many benefits to be realized from this effort – protection of the public health and safety, preservation of essential services, prevention of property damage, and prevention of the local economic base, to mention just a few – will help ensure that Sheridan County and all of its communities remain vibrant, safe, and enjoyable places in which to live, raise a family and conduct business.

1 Federal Emergency Management Agency’s Five Mission Areas - http://www.fema.gov/mission-areas

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2.0 Mitigation Strategy

Sheridan County and participating jurisdictions developed a strong mitigation strategy in the 2009 Sheridan County Multi-Hazard Mitigation plan which serves as the long-term blueprint for reducing the potential losses identified in the risk assessment sections of this plan. The mitigation strategy describes how the community will accomplish the overall purpose, or mission, of the planning process. The 2013 Planning Team reviewed the 2009 mitigation strategy and goals and has determined they continue to be relevant to Sheridan County and participating jurisdictions. Additional details regarding the Sheridan County mitigation strategy are presented at the end of this plan in a section titled, Mitigation Strategy and Mitigation Actions. Sheridan County’s mitigation strategy contains identified mitigation actions which are tied to specific projects and activities that help achieve the goals2. This update also documents the mitigation actions which have been completed for Sheridan County and participating jurisdictions.

Purpose of the Sheridan County Multi-Hazard Mitigation Plan The purpose for developing this plan is to identify activities which if implemented can eliminate or reduce the risk residents of the county face from natural and man-made threats or hazards. The county has been negatively affected by a variety of natural and man-made hazards, with property damaged and lives threatened. Some hazards occur throughout the county and others are localized. This plan addresses the unincorporated and incorporated areas of Sheridan County. The incorporated areas include Sheridan, Dayton, Ranchester and Clearmont. Future mitigation projects are identified for the county as well as those four communities. The plan meets planning criteria established for local mitigation plans, pursuant to the Disaster Mitigation Act of 2000, as detailed in Title 44 Code of Federal Regulations, § 201.6. Adopting jurisdictions are eligible to apply for Pre-Disaster Mitigation (PDM) and Hazard Mitigation Grant Program (HMGP) funding.

Authority The Sheridan County Multi-Hazard Mitigation plan has been adopted by Sheridan County, City of Sheridan, Town of Dayton, Town of Clearmont, and Town of Ranchester in accordance with the authority granted to counties by the State of Wyoming. The Sheridan County Emergency Management Coordinator is the lead position that was responsible for coordinating this update which followed the recommendations of the Federal Emergency Management Agency (FEMA) Local Mitigation Planning Handbook (March 2013). The original 2009 Sheridan County Multi-Hazard Mitigation Plan as well as this update were developed in accordance to the Robert T. Stafford Disaster Relief and Emergency Assistance Act, 42 U.S.C., Section 322, Mitigation Planning, as enacted by Section 104 of the Disaster Mitigation Act of 2000 (P.L. 106-390) and by FEMA’s Interim Final Rule published in the Federal Register on February 26, 2002, at 44 CFR Part 201.

2 Federal Emergency Management Agency (FEMA) Local Mitigation Planning Handbook, March 2013

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Each participating community in the 2014 Sheridan County Multi-Hazard Mitigation Plan has existing

local authorities, policies, programs, and resources in place that support the local efforts of hazard

mitigation. Below is a list of resources for each participating community in this plan update.

Town of Clearmont

Flood Damage Prevention Ordinance Adopted January 2014.

Town of Clearmont enrolled NFIP effective February 2014

GPS Mapping Project approved February 2014. (project will start March or April 2014)

Volunteer First responders have been trained and continue to enhance their training and are pursuing additional volunteers to be trained

Plan to review and update current town ordinances

Town of Dayton

The Town of Dayton currently has Flood Hazard Regulations in place and practices zoning and enforcement requirements under the National Flood Insurance Program (Ordinance Title 15, Chapter 15.04)

The Town of Dayton also has a Flood Damage Prevention Ordinance in place to regulate under the requirements of the National Flood Insurance Program (Ordinance Title 15, Chapter 15.08)

The Zoning Administrator for the Town of Dayton is responsible for enforcing all required building and zoning permits for the Town of Dayton as stipulated in local ordinance title 17

Town of Ranchester

Ranchester has adopted the required ordinance and map to allow participation in the NFIP

City of Sheridan

The City of Sheridan has several divisions that support each other in the development of local policies, programs, and resources which have an impact on local community planning and hazard mitigation.

The Planning Division The Planning Division reviews, approves, and issues permits for public and private projects related to improvements and grading, subdivision, right-of-way encroachment, annexations and sign permits. It also supports the City of Sheridan’s community economic development initiatives.

Building Division The Building Division is an excellent community resource who reviews plans, issues permits, and provides inspections for several different types of public and private building projects.

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Engineering Division The Engineering Division is responsible for fulfilling the City of Sheridan’s capital improvement plan, as well as traffic, flood plain administration, flood control, and management of several different local, state, and federal funding resources.

Sheridan County

Sheridan County Planning and Zoning Department Sheridan County Planning and Zoning Department is responsible for long-range plans in the county including the Sheridan County Comprehensive Plan. Elements of the Comprehensive Plan include Land Use, Transportation, County Utilities, Sensitive Areas, Natural & Man made Hazards, and Open Space. The Sheridan County Comprehensive Plan can be downloaded from the Sheridan County Planning and Zoning website (http://www.sheridancounty.com/info/pw-plan/complan.php). The Sheridan County Comprehensive plan presents several GIS mapping applications for future planning in identified hazard areas as well as outlines specific hazard profile information for areas in the county. The GIS hazard map presented in the Sheridan County Comprehensive Plan displays hazard area for the pre-2013 100 year floodplain, landslide hazard areas, faults, abandoned mines and knows subsidence areas. This is a complimenting document to the Sheridan County Multi-Hazard Mitigation Plan and presents the appropriate permitting and zoning regulations required by Sheridan County. This plan was developed in 2009.

o Sheridan County Planning Department is also responsible for permitting under the Sheridan County Land Use Regulations including Rezoning, Quarry, Variance, Conditional Use permits, Subdivision permits and exemptions, and Mobile Home Park Licenses.

SAWSJPB is the rural water system surrounding the City of Sheridan. The Sheridan County Public Works office, processes applications to connect to the water system, prepare water service agreements with developers, and administer board business

Code Enforcement Officers The Sheridan County Code Enforcement Officers are responsible for ensuring private property and construction and development projects conform to zoning regulations and review conditions of approval, and issue zoning permits. We are also responsible for inspections, investigations, and resolution of zoning enforcement issues.

Road and Bridge Department Road & Bridge is responsible for road maintenance, minor bridge repair snow removal, and culvert installation.

Sheridan County Public Works Department The Sheridan County Public Works Department permits several activities in Sheridan County:

o Building Permit & Zoning Permit: Construction of any new building, or addition to, or change of use of existing building.

o Driveway Permit: Change or construction of any driveway accessing a County Road. o Septic Permit: Construction of a new or replacement septic system, including a partial

replacement.

http://www.sheridancounty.com/info/pw-plan/complan.php

http://www.sheridancounty.com/info/pw-plan/complan.php

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o Flood Plain Program Development Permit: Any activity within the County designated flood plain areas.

Sheridan County Flood Hazard Standards o The purpose of these rules is to minimize public and private losses due to flood

conditions and to promote the health, safety and general welfare of the public. The Standards discuss permitting requirements, the responsibility of persons when constructing new homes or making improvements to existing homes, standards for subdivision development, procedures for appeals/variances as well as other policies and standards for development that will occur in special flood hazard areas. The resolution requires that certain building techniques be followed to protect against or minimize flooding hazards.

Goals The Federal Emergency Management Agency (FEMA) defines mitigation goals as general guidelines that explain what the community wants to achieve with the plan. They are usually broad policy-type statements that are long-term, and they represent visions for reducing or avoiding losses from the identified hazards.

The following goals are part of the Sheridan County multi-hazard mitigation strategy for reducing loss of life and property damage from natural and man-made hazards. The goals are based on the vulnerabilities identified in the risk assessment portion of the plan and were developed by the Sheridan County Emergency Management Office and reviewed and endorsed by the Sheridan County Local Emergency Planning Committee (LEPC) in 2009 and approved by the planning team in 2013.

1. Mitigate the effect of hazards through education, ordinances, resolutions, and clear definition and implementation of mitigation projects to reduce the loss of property and enhance life-safety of residents.

2. Coordinate mitigation activities with all entities of Sheridan County to assess the hazards and take various actions to reduce or eliminate the risk factors of those hazards.

3. Reduce the economic impact on the local economy caused by the effects of hazards in the communities.

3.0 Funding

Funding for the 2013 Sheridan County Multi-Hazard Mitigation Plan Update was provided by the FY12 State Homeland Security Program Grant. The State Homeland Security Program supports the implementation of State Homeland Security Strategies to address the identified planning, organization, organization, equipment, training, and exercise needs to prevent, protect against, mitigate, respond to, and recover from acts of terrorism and other catastrophic events.

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4.0 Planning Process The Sheridan County Multi-Hazard Mitigation Plan examines multi-hazard probabilities and determines needed mitigations projects. Emphasis has been placed on hazards that have the potential for the greatest impact on the community as identified through a hazard analysis conducted by the 2009 and 2013 planning teams. The 2013 planning team reviewed and approved of the 2009 planning process utilized in the development of the original Sheridan County Multi-Hazard Mitigation Plan and decided to support the original planning process by following it for the update. The original Planning Process consisted of the following six steps:

1. Identification of Hazards and Risk Assessment 2. Identification and definition of mitigation goals and objectives 3. Identification of mitigation projects 4. Selection of filtering/ranking criteria 5. Establishment of the plan maintenance procedure 6. Preparation and review of a draft plan

The Sheridan County Multi-Hazard Mitigation Plan update was conducted in an open manner involving community stakeholders from Local, State and Federal agencies. The plan updated consisted of the following steps to meet/exceed the FEMA requirements for local mitigation planning as defined by the Robert T. Stafford Disaster Relief and Emergency Assistance Act and by FEMA’s Interim Final Rule published in the Federal Register on February 26, 2002, at 44 CFR Part 201. Planning process meeting handouts, presentations, and minutes can be found in Appendix C: Meeting Documentation and Worksheets.

1. Kick Off Meeting3 Goals of the meeting included but were not limited to the following actions:

• Assemble Planning Team and Identify Potential New Members4 • Conduct a detailed review of 2009 Sheridan County Multi-Hazard Mitigation Plan by

revisiting the original planning process, goal, mitigation strategy, hazard risk assessments and ranking criteria.

• Planning team members also identified local plans, studies, and community capabilities that have been utilized to update and enhance the Sheridan County Multi-Hazard Mitigation Plan.

2. Start Outreach Strategy focused on Stakeholder Participation throughout the update process5 3. Conduct a detailed review and update of existing Hazard, Risk, and Vulnerability assessments 4. Flood Planning Team Stakeholder Meeting, Wildland Fire Planning Team Stakeholder Meeting,

Local Emergency Planning Committee Presentation and Discussion Meeting6 5. Submit updated Risk Assessments to Planning Team(s) and Public for review and comment as

they are completed 6. Submit final draft to Sheridan County Emergency Management

3 2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix C - Meeting Documentation and Worksheets

4 2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix A - Team Members

5 2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix D - Public Outreach

6 2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix C - Meeting Documentation and Worksheets

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7. Provide final plan to Wyoming Office of Homeland Security with completed FEMA Local Plan Review Guide

8. Provide Final Updated Plan to FEMA Mitigation Division with completed FEMA Local Plan Review Guide

9. Present Updated Sheridan County Multi-Hazard Mitigation Plan to Sheridan County and participating Jurisdictions for adoption

The Planning Team(s) for the 2013 Sheridan County Multi-Hazard Mitigation Plan was led by the Sheridan County Emergency Management Office and selected contractor, Ayres Associates. Sheridan County, City of Sheridan, Town of Clearmont, Town of Dayton, and Town of Ranchester planning team members where identified by Letters of Intent to participate in the plan update7. There was a Core Planning Group that consisted of Local, State, and Federal contributing stakeholders, Table 1. The Flood and Wildland Fire team members where identified at the Kick Off meeting and through the community capability assessment (Tables 2 and 3). An extensive list of Local, State, and Federal stakeholders can be found in Appendix A – Planning Team. All planning team members where contacted throughout the Plan update process and invited to participate by contributing information, insight, reviews, and comments to the Sheridan County Multi-Hazard Mitigation Plan. Plan section updated were shared directly with the planning groups and posted on the Sheridan County website as they became available for an efficient review and comment process. Specific planning team members participated in different capacities throughout the plan update process. Everyone had access to and was invited to participate in reviewing hazard risk profiles and participating in planning team meetings through the plan update process. Specific Core Planning Team Stakeholders, Flood and Wildland Fire Team Stakeholders represented all participating jurisdictions and details regarding contributions and meeting attendance can be found in Appendix C - Meeting Documentation and Worksheets. The Town of Clearmont held a separate hazard mitigation focused meeting on February 17, 2014 to discuss the current and future role of the Town of Clearmont in the Sheridan County Multi-Hazard Mitigation Plan and identified hazard actions. The Town of Clearmont will continue to participate in the mitigation plan and has submitted meeting minutes and specific hazard implementation actions for their community which have been integrated into this plan update and can also be found in Appendix C: Meeting Documentation.

Table 1: Core Planning Team Stakeholders

Name Title Agency

Terry Lenhart Fire Chief Sheridan Fire-Rescue

Tom Manolis Water Superintendent City of Sheridan

Peter Clark Councilman Town of Ranchester

Dave Coleman Coordinator Sheridan County Emergency Management

7 2013 Sheridan County Multi-Hazard Mitigation Plan Appendix B - Letters of Intent

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Rod Liesinger Sheridan County Public Works Department

Sheridan County

Bob Wood Town of Dayton, Mayor

Town of Dayton

Steve Small Sheridan County LEPC Chairman

Sheridan County Emergency Management

Terry Cram County Commissioner Sheridan County

Steve Small LEPC Chairman Sheridan County

Kody Lamb Sheridan PD City of Sheridan

Jamie Ringley Sheridan County Fairgrounds

Sheridan County

Roy Harper BNSF National

Susan Mickelson WY. Dept. of Agriculture

State of Wyoming Dept. of Agriculture

Jacob Arnold WY ARNG State of Wyoming ARN

James Rader Sheridan Memorial Hospital

Sheridan County

Jim Marchese Member of the public Member of the Public

Michael Rogers Sheridan County Sheriff’s Office

Sheridan County

Melinda Gibson SHMO Wyoming Office of Homeland Security

Ginni Melton NFIP Coordinator Wyoming Office of Homeland Security

Kim Johnson Governmental Liaison Wyoming Office of Homeland Security

Tony Bergantino

Service Climatologist/Wyoming CoCoRaHS State Coordinator

Water Resources Data System – Wyoming State Climate Office

Paul Wright District Forester State of Wyoming Forestry Division

Milk Hand Safety of Dams Engineer

Wyoming State Engineers Office

Seth Wittke Manager/Geologic Hazards

State of Wyoming Geological Survey

Martin Larsen Geologic Hazards/Mapping

State of Wyoming Geological Survey

Jon Warder Fire/Fuels/Safety Bighorn National Forest

United States Forest Service (USFA)

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Kirk Strom Fire Ecologist High Plains District BLM

Bureau of Land Management (BLM)

Tom Frieders Warning Coordination Meteorologist

National Weather Service

Carrie Chitty Project Manager Ayres Associates

Gene MacDonald Project Manager Ayres Associates

Table 2: Flood Planning Team Stakeholders

Name Title Agency

Peter Clark Council Member Town of Ranchester

Dave Coleman Coordinator SCEMA

Rod Liesinger PW Director Sheridan County

Tom Manolis Water

Superintendent City of Sheridan

Lane Thompson City Engineer City of Sheridan

Chris Johnson Town Engineer Town of Ranchester



Table 3: Wildland Fire Planning Team Stakeholders

Name Title Agency

Mike Mackey Grants Admin Sheridan County

Dave Coleman Coordinator SCEMA

William Biastoch County Fire Warden Sheridan County

Paul Wright District Forester Wy State Forestry Division

Mark Reed County Planner Sheridan County

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Terry Lenhart Fire Chief Sheridan County



5.0 Community Profile

Sheridan County encompasses approximately 2,523 square miles and is located in the north-central Wyoming. The County shares its northern border with Montana. Table 2 and Figure 2 present the population distribution and growth rate from 1990-2012 for Sheridan County and incorporated communities. In 2012 there was an estimated population of 26,596. According to the U.S Census Bureau, all incorporated cities and towns in Sheridan County experienced population grown with the exception of the Town of Clearmont. There was a 2% population increase for unincorporated Sheridan County, 5% increase for the Town of Ranchester, 3% for the Town of Dayton, 1% for the City of Sheridan and a 0% population growth for the Town of Clearmont between 1990 and 2012. Within its boundaries lie the incorporated City of Sheridan and Towns of Dayton, Clearmont, and Ranchester (Figure 1). The topography ranges from high plains in the eastern part of the County to the high peaks of the Bighorn Mountains in the western half of the County. Several creeks drain to the northeast off the Big Horn Mountains. Clear Creek runs northeasterly through the eastern County. Interstate 90 runs through the middle of the County along the foothills of the Big Horn Mountains. Oil and gas, ranching, industry, and tourism are the main financial stay of the county.

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Figure 1: Overview map of Sheridan County and Participating Jurisdictions in the 2013 Sheridan

County Multi-Hazard Mitigation Plan

Table 2: Population Distribution and Growth Rate 1990-20128

City of

Sheridan Town of Dayton

Town of Clearmont

Town of Ranchester

Unincorporated Sheridan County

1990 14,025 571 119 681 26,562

Percent Change 1990-2000 13% 22% -3% 3% 0%

2000 15,899 695 115 702 26,560

Percent Change 2000-2010 10% 9% 23% 22% 10%

2010 17,444 757 142 855 29,116

Percent Change 2010-2012 1% 3% 0% 5% 2%

2012 17,698 777 142 898 29,596

1990-2012 Percent Change 1% 3% 0% 5% 2%

8 U.S Census Bureau Population Statistics, Last update 4/9/2013

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Figure 2: Population Growth Charts for Sheridan County, City of Sheridan, Town of Ranchester, Town

of Dayton, and Town of Clearmont

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6.0 Development Trends in Sheridan County The majority of the developed land in the county is located in incorporated cities and towns, particularly in the City of Sheridan and its growth area. It is not surprising that agriculture is the largest existing county land use by area at just over 996,597 acres (about 62%). Public lands account for the next largest land use at 572,399 acres (approximately 36%). Residential land use accounts for 21,072 acres (1.3%), with over 16,000 acres of built residential outside Sheridan’s Urban Service Area, and nonresidential uses (businesses, industry, special purpose, and multi-use) account for another 3,034 acres (less than one percent) and tend to be located near existing communities. The county has 14,753 acres of land (less than one percent) classified as vacant. Sheridan County continues to have major growth between the City of Sheridan and the Town of Big Horn where much of this growth is in the vicinity of the Little Goose Creek which poses a major flooding issue. This growth is expected to continue for many years to come. Another area where growth is occurring is west of the City of Sheridan along the Big Goose Creek which would also pose a possible flooding issue. Sheridan County also has minor growth patterns throughout the County as Sheridan County has become a haven for people looking to live the country style of living away from the major populated areas of the country. Some of these residences are in remote areas of the County and are at risk from Wildland fires and possibly tornadoes.

7.0 Community Capability Assessment The planning team identified local mitigation capabilities throughout the planning process. Community capabilities are existing authorities, policies, programs, and resources that reduce hazard impacts or that could be used to implement hazard mitigation activities. Table 3 presents the Sheridan County Community Capabilities identified through the planning process and utilized throughout the 2013 Sheridan County Multi-Hazard Mitigation Plan update.

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Table 3: Sheridan County Community Capabilities

Title: Sheridan County Comprehensive Plan

Date of Last Revision: 2009

Author/Owner: Sheridan County, WY

Description: The Comprehensive Plan is the overall policy guide for future growth and development.

Relationship to Natural Hazard Mitigation Planning:

This plan outlines development practices, regulations, and requirements for Sheridan County. The Sheridan County Comprehensive Plan includes a Hazard Assessment for 100-Year floodplain, steep slope areas (20% or greater), landslide areas, faults, abandoned mine sites, and known subsidence areas.

Title: Sheridan County Flood Hazard Standards



Title: Sheridan County Wildland Fire Mitigation Plan



Description: Plan establishes a process and addresses issues such as wildfire potential, hazard mitigation, and community preparedness, response to the incident and structure protection.


Wildland fire hazard risk assessment and Wildland Urban Interface risk

Title: Western State Wildland Urban Interface Grant: Cost-Share Practices and Rates

Date of Last Revision: 5/29/2013

Author/Owner: Wyoming State Forestry Division and United States Forest Service

Description: Grant program reimbursement and procedures

Relationship to Natural Hazard Mitigation Planning: Wildland Fire Mitigation Funding Source

Title: Sheridan County Fuel Mitigation Narrative: American Recovery and Reinvestment Act

Date of Last Revision: Author/Owner: Wyoming State Forestry Division

Description: One time grant funds to mitigate wildland fire risks in Sheridan County

Relationship to Natural Hazard Mitigation Planning: Wildland Fire Mitigation Funding Source

Title: Flood Risk Report, Sheridan County

Date of Last Revision: 3/29/2013

Author/Owner: Federal Emergency Management Agency (FEMA)

Description: Non‐regulatory information on flood risk in Sheridan County, Wyoming


Presents key risk analysis data for Sheridan County, the City of Sheridan, Town of Dayton, Town of Ranchester, and Town of Clearmont and discusses areas of mitigation interest.

16

Title: Flood Insurance Study, Sheridan County and Incorporated Areas

Date of Last Revision: Preliminary 2012 and Final January 2014

Author/Owner: Federal Emergency Management Agency (FEMA)

Description: Regulatory information on flood risk in Sheridan County, Wyoming


Flood hazard data for floodplain management and flood insurance purposes for Sheridan County, the City of Sheridan, Town of Dayton, Town of Ranchester, and Town of Clearmont and discusses areas of mitigation interest.

8.0 Plan Implementation, Integration and Maintenance Procedures The 2013 Sheridan County Multi-Hazard Mitigation Planning team made a minor change to the Plan

Implementation and Maintenance sections. In the 2009 plan, the Sheridan County Local Emergency

Planning in Committee (LEPC) was identified as the central responsible group for implementation,

integration and maintenance of the Sheridan County Multi-Hazard Mitigation Plan. After considerable

consideration and discussion, the 2013 Sheridan County Multi-Hazard Planning team identified a more

efficient and realistic approach for the implementation, integration and maintenance of the Sheridan

County Multi-Hazard Mitigation plan9. The Sheridan County Emergency Management Coordinator with

the support of the Local Emergency Planning Committee (LEPC), Sheridan County, City of Sheridan,

Town of Dayton, Town of Ranchester, and Town of Clearmont will be responsible for implementation,

integration and maintenance of this plan. By identifying the Sheridan County Emergency Management

Coordinator as the plan representative it designates one point of contact and organizing force for the

success for the implementation of identified mitigation actions that support the overall all mitigation

strategy.

Implementation The Sheridan County Emergency Management Coordinator with the support of the Local Emergency

Planning Committee (LEPC), Sheridan County, City of Sheridan, Town of Dayton, Town of Ranchester,

and Town of Clearmont will be responsible for implementation of this plan through the detailed

integration and maintenance sections outlined below.

Integration The Sheridan County Emergency Management Coordinator with the support of the Sheridan County

Local Emergency Planning Committee (LEPC) and representatives from participating jurisdictions have

determine the hazard mitigation goals and strategies identified in the 2013 Sheridan County Multi-

Hazard Mitigation Plan support community goals to address such issues as; economic development,

subdivision ordinances, capital improvement, building permits, growth management, sustainability,

environmental preservation, historic preservation, redevelopment, health and/or safety, recreation, or

transportation. The original 2009 Sheridan County Multi-Hazard Mitigation Plan identified an

9 2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix C: Meeting Documentation and Worksheets

17

integration strategy that continues to be relevant in this plan update. The current integration strategy

that has been and will continue to be implemented has the purpose of:

• Determining if the mitigation plan is compatible with goals stated in other plans

• Identify mitigation initiatives or proposed projects which serve multiple objectives for the

communities and could be included in multiple plans

• Identify needs for revision or updating to the mitigation plan, or other plans, to provide a more

comprehensive approach to hazard mitigation (including addition of new mitigation measures)

The following plans have been identified by 2013 Sheridan County Multi-Hazard Mitigation Planning

teams as relevant resources for community information, hazard profile information, mitigation project

identification and general community development tools:

• Sheridan County Comprehensive Plan (2009) • Sheridan County Wildland Fire Mitigation Plan (2009) • State Forestry Division Wildland Fire Reports • Federal Emergency Management Agency (FEMA) Flood Risk Report for Sheridan County

(2013) • Federal Emergency Management Agency (FEMA) Flood Insurance Study for Sheridan

County (2014) • Sheridan County Community Wildfire Protection Plan (2004) • BLM Fire Protections Plan • Sheridan Fire District Plan • Plans maintained by the Natural Resource Conservation Services, USDA

In addition to the integration steps listed above, each participating community in the Sheridan County Multi-Hazard Mitigation Plan Update has identified ways they will locally integrate this plan over the next 5-years.

Town of Clearmont

Mitigation plan will be incorporated into other plans as opportunities allow and time permits.

Clearmont participates in County Plans, (County EOP, etc) and the mitigation plan will be

incorporated within the county plans

Town of Ranchester

The Town of Ranchester will ensure through our flood prevention ordinance along with FEMA provided GIS flood mapping (NFHL) that development in the flood plain is only allowed by flood plain development permit.

Town of Dayton

The Town of Dayton will continue to enforce the local flood protection measures required by the National Flood Insurance Program.

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City of Sheridan

Local efforts will be made to include the Sheridan County Multi-Hazard Mitigation plan and incorporate hazard profile information and mitigation actions into local planning documents and meetings.

Sheridan County

Sheridan County will make efforts to include the Sheridan County Multi-Hazard Mitigation plan and into county planning documents in the future. There is currently a plan to identify funding to begin updating the Sheridan County Comprehensive Plan and the 2014 Sheridan County Multi-Hazard Mitigation Plan hazard profile information will be referenced and included when appropriate.

New flood hazard mapping GIS layer will be used in the next 5 years to enforce flood ordinance and building codes.

The County will continue to utilize the existing GIS hazard mapping layers provided by the Wyoming Geological Survey in 2009 when the original Sheridan County Multi-Hazard Mitigation Plan was developed to research development permits and applications and to regulate building in identified hazard areas.

Additional integration of the Sheridan County Multi-Hazard Mitigation Plan may be utilized by the Bureau of Land Management Office located in Sheridan County for Fire Mitigation planning efforts.

Maintenance The Sheridan County Emergency Management Coordinator will act as a countywide liaison to coordinate

Sheridan County and participating jurisdictions to complete mitigation plan reviews, incorporate new

mitigation strategies and conduct 5 year updates. The Sheridan County Emergency Manager will utilize

the Annual Review worksheet to track annual review dates and extreme hazard or weather events

(Table 4). Updates to the Sheridan County Multi-Hazard Mitigation Plan can be made as needed at any

time after the initial FEMA approval date, including immediate updates subsequent to disasters.

Jurisdictions who adopt the Plan will be eligible to apply for Hazard Mitigation Assistance (HMA) grant

funds which includes Hazard Mitigation Grant Program (HMGP) and Pre-Disaster Mitigation (PDM)

program funding. The Sheridan County Emergency Management Coordinator will document revisions

and updates made to the Plan by maintaining records of public announcements, meetings and contacts

relevant to goals and identified hazards in the Sheridan County Multi-Hazard Mitigation Plan. Table 5

presents a suggested schedule for meeting the State and FEMA Hazard Mitigation Assistance (HMA)

program guidance and approval timelines.

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Table 4: Sheridan County Multi-Hazard Mitigation Plan Monitoring Worksheet

This worksheet should be updated annually or as events occur

2014 Date of Review:

Hazard or Extreme Weather Events:









Table 5: Suggested Schedule for Updating the Sheridan County Multi-Hazard Mitigation Plan

Initial Plan Approval Date 3/13/2009 5 Year Expiration Date 3/13/2013 Submit to WOHS by: 11/11/2013

Submit to FEMA by: 1/6/2014

2014 Approval Date April 2014 Fall/Winter 2014 Plan Review November 2014

Summer 2015 Plan Review August 2015

Summer 2016 Plan Review and Plan Update Funding Source Identified with possible FEMA HMA/PDM Planning Application Submitted August 2016

Summer 2017 Plan Review and Update Kick Off August 2017

Spring 2018 Plan Update Continued March 2018

5 Year Expiration Date April 2019 Submit to WOHS by: December, 2018

Submit to FEMA by: February, 2019

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The Sheridan County Emergency Management Coordinator will coordinate representatives from Sheridan County and participating jurisdictions to conduct reviews of the Sheridan County Multi-Hazard Mitigation plan and incorporate the following eight steps:

1. Review required Local Hazard Mitigation Planning guidance documents and best available guidance provided by the State of Wyoming and Federal Emergency Management Agency (FEMA) relevant to Local Hazard Mitigation Plan Updates.

2. Examine and revise the Risk Assessments for Sheridan County and participating jurisdictions to ensure they are current. New information, maps, and GIS data will be incorporated into hazard profiles as needed. Local, State and contracted hazard experts will validate profiles, as necessary.

3. Evaluate mitigation strategies, including progress on goals and implementation of proposed mitigation projects and measures listed in the Plan.

4. Include documentation of local disasters and incorporate post-disaster mitigation report findings as appropriate, including addition of recommended mitigation measures, policies, etc.

5. Identify problems (technical, legal, financial, or other) that hinder or otherwise affect implementation of the plan and recommend action steps for resolving these issues.

6. Coordinate with all participating jurisdictions and planning partners (government, business/industry, private organizations, etc.) identifies in the Plan to ensure continuation of community involvement and support.

7. Integrate Plan with other community plans. Refer to Integration section for additional guidance and procedures. The Sheridan County Multi-Hazard Mitigation Plan will be integrated into local and countywide community planning efforts.

8. Prepare and submit report of Plan update and revisions to elected officials.

9.0 Public Participation Federal regulations require “Public Participation” in the review and update process of local hazard mitigation planning efforts. “Public” is defined as individuals other than representatives of government agencies. Members of the public have been encouraged to participate in planning meetings for the 2013 Plan update and are encouraged to participate in annual reviews of this plan by contacting the Sheridan County Emergency Management Coordinator. Updates regarding the Sheridan County Multi-Hazard Mitigation plan will be posted on the Sheridan County Public Announcement webpage and also announced at the Local Emergency Planning Committee (LEPC) monthly meetings. For this plan update the Press, a Sheridan County newspaper profiled the 2013 update efforts and encouraged community support and input in an informative newspaper article10 In the Federal Emergency Management Agency (FEMA) approved 2009 Sheridan County Multi-Hazard Mitigation Plan it stated that at least one Local Emergency Planning Committee (LEPC), or other public mitigation planning meeting, would be held with the primary purpose of reviewing the existing plan. Since 2009, no specific meeting has been held to review the 2009 approved plan. The FEMA approved plan was reviewed in detail starting with the 2013 Sheridan County Multi-Hazard Mitigation Plan update effort which included a multi-jurisdictional public meeting, a Wildland and Flood team breakout meetings, and a LEPC meeting. Updates regarding the 2013 plan update process were posted on the

10

2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix D - Public Outreach

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Sheridan County Public Announcement webpage and were shared with planning team members though out the plan update process11.

10.0 Hazard Identification In 2009, Sheridan County Emergency Management along with the Wyoming State Geological Survey identified 17 potential hazards that could affect Sheridan County, 12 of which were considered to be significant and potentially life threatening. The 12 potential hazards where defined and explanations provided in the 2009 Sheridan County Multi-Hazard Mitigation Plan. The 2013 Sheridan County Multi-Hazard Mitigation Plan has enhanced several sections of the Sheridan County Multi-Hazard Mitigation Plan by including new hazard profile information, more descriptive definitions, updated hazard event tables, and specific mitigation actions which support the overall goals of this plan. There is also a new section that has been incorporated after being identified as a potential hazard by the 2013 Planning Team, Man-Made hazards.

Dam Failure: Dam failure is the uncontrolled release of impounded water resulting in

downstream flooding, which can affect life and property. Flooding, earthquakes, blockages,

landslides, lack of maintenance, improper operation, poor construction, vandalism, or

terrorism can cause dam failures.

Drought: Drought is described as a protracted period of deficient precipitation resulting in

extensive damage to vegetation.

Earthquake: A sudden motion or trembling that is caused by a release of strain

accumulated within or along the edge of the earth’s tectonic plates.

Flood / Flash Flood/Ice Jam: A general and temporary condition of partial or complete

inundation of normally dry land areas from (1) the overflow of inland waters or, (2) the

unusual and rapid accumulation or runoff of surface waters from any source, or (3)

mudflows or the sudden collapse of shoreline land. Flash flood: a flood event occurring

with little or no warning where water levels rise at an extremely fast rate. An ice jam is a

stationary accumulation of ice that restricts water flow.

Hail: Hail is ice that forms, grows and ultimately falls from thunderclouds. Severe storms can drop enough hail to blanket the ground, flatten crops or clog storm sewers. Hazardous Materials: As defined by the U.S. Department of Transportation (DOT), is one that poses an unreasonable risk to health and safety of operating or emergency personnel, the public, and/or the environment if not properly controlled during handling, storage, manufacture, processing, packaging, use, disposal, or transportation.

11

2013 Sheridan County Multi-Hazard Mitigation Plan, Appendix C: Public Outreach Documentation

22

Landslide: A downward movement of a slope and materials under the force of gravity.

Lightning: Lightning is a sudden electrical discharge released from the atmosphere that follows a course from cloud to ground, cloud to cloud, or cloud to surrounding air, with light illuminating its path. Lightning’s unpredictable nature causes it to be one of the most feared and deadly weather elements. Man-made Hazards: Man-made Hazards can be technological hazards and/or acts of terrorism. This plan references the Federal Emergency Management Agency (FEMA) definition of man-made hazards and highlights their distinction from natural hazards primarily in that they originate from human activity. In contrast, while the risks presented by natural hazards may be increased or decreased as a result of human activity, they are not inherently human induced. Severe Winter Storm: A winter storm can range from a moderate snow over a few hours to blizzard conditions with blinding wind-driven snow that lasts several days.

Tornadoes: Tornadoes are violently rotating column of air extending from a thunderstorm

to the ground.

Wildfire: An uncontrolled fire spreading through vegetation fuels, exposing and possibly

consuming structures.

11.0 Hazards Risk Analysis Based on the histories and potential future occurrences of hazards that may cause significant impacts in Sheridan County, the LEPC selected the following to be addressed in more detail in the hazard-specific chapters of this plan: dam failures, droughts, earthquakes, floods, hail, landslides, lightning, man-made hazards, mine subsidence, tornadoes, wildfire, winter storms, and hazardous material spills. Hazards that were not addressed further were those that were not likely to occur in the next 100 years or those that have not had a historical impact on property or life safety. At the end of each of the hazard-specific chapters there is a summary of the risk to people and property for each hazard. Table 6 presents the current hazard summary analysis for all identified hazards in Sheridan County currently analyzed in this plan. The probability of the hazard occurring is assessed as well. In 2009, the Planning team generated a ranking of hazards to determine the most significant potential threats posed by natural and man-made hazards. The hazard analysis presented in the plan is based on a high, medium and low level of risk, as defined below, based on past history and the potential for future occurrence.

High: This ranking carries the highest threat. The potential of this hazard occurring in the assessment area is considered a matter of “when” it will occur, as opposed to “if” it will occur. The potential for damage is widespread. Hazards in this category may have already occurred in the past.

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Medium: This ranking carries a moderate threat level to the general population. The potential of occurrence may be the same as the “high” ranking but the potential damage is more isolated and less costly than a more widespread disaster. Low: The lowest ranking in the survey, the occurrence and potential cost of damage to life and property is minimal. Jurisdiction(s) Affected: This indicates how widespread the hazard is within the county, and where the risk varies across the planning area.

Table 6: Current Hazard Summary Table

Hazard Property Affected

Population Affected

Probability Jurisdiction

Dam Failure High High Low Sheridan, Dayton, Ranchester, Portions of unincorporated County

Drought High High Medium County

Earthquake Low Medium Low County

Flood/Flash Flood High Medium Medium City of Sheridan, Dayton, Ranchester, portions of the unincorporated county

Hail Medium Medium Medium County

Hazardous Materials Low Medium Medium County

Landslide Medium Low Medium Portions of central and western unincorporated County, Sheridan area

Lightning Low Low High County

Mine Subsidence Low Low Medium Unincorporated County

Tornadoes Medium Medium Low All

Severe Winter Storm Medium High High County

Wildfire High Medium High Dayton, Sheridan, Clearmont, portions of unincorporated county

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Dam Failure

Summary of Dam Failure Section Update • Expansion of definition of 'Dam' and Dam Failure Risks as related to Floods

• New Mitigation Actions Section which indicates appropriate Dam Failure Mitigation Measures.

• Updated Location and Hazard Ranking of Dams in Sheridan County

• Updated Dam Failure History Section

• Updated Wyoming State Engineers Office Dam Safety Program Data

• This section was reformatted to complement the overall goals of the Sheridan County Multi-Hazard Mitigation Plan Update

Dam Failure12

A dam is a barrier built across a waterway for impounding water. Dams can be formed by human agency, natural causes, or even by the intervention of wildlife such as beavers. Man‐made dams are typically classified according to their size (height), intended purpose, or structure. The majority of dams in the United States are privately owned and operated. Most dams are regulated by federal or state agencies; these agencies may require and retain copies of Emergency Action Plans (EAP) for high hazard dams. EAPs contain flood inundation maps for fair weather breach and breach during probable maximum flood. Dams are classified based upon hazard potential. This classification is based on the consequences if a dam were to fail, not on the potential of failure, or the existing condition of the dam13. The dams were rated (1) high, (2) significant, and (3) low hazard. The Corps of Engineers based the hazard potential designation on such items as acre-feet capacity of the dam, distance from nearest community downstream, population density of the community, and age of the dam. High hazard dams would, in case of failure of the dam, likely cause loss of life. Significant hazard dams would, in case of failure, likely cause significant property damage, but no loss of life. Failure of a low hazard dam would likely cause only minimal property damage. As stated in the 2013 State of Wyoming Dam Failure section, hazard potential classification is no guarantee of safety. There are 128 dams in Sheridan County; 124 are privately owned and operated, 2 are local, and 2 are federal. 7 of these had a high hazard rating as of 2012 (Figure 1). Dams can cause the following problems related to flood risk:

12

The FEMA Flood Risk Report for Sheridan County referenced in this plan update was considered final on March 29, 2013. 13

State of Wyoming Dam Failure Section, October 2013 Draft Update provide by the Wyoming Office of Homeland Security

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Older dams in some parts of the country are constructed using an assortment of materials.

These structures may not have adequate capacity to release water and could be overtopped, which could result in failure.

Development may occur in the dam’s flood inundation zone and the downstream risk and hazard classification may have changed since the dam was constructed.

For larger dams, a flood easement may have been obtained on a property upstream or downstream of the dam. However, there may have been buildings constructed in violation of the flood easement.

When a new dam is constructed, the placement of material in a floodplain can alter how the watercourse flows. This can result in flooding upstream, downstream, or both.

Figure 1: Location and Hazard Ranking of Dams in Sheridan County14

History

There have been a number of dam failures in Wyoming, some of which have caused the loss of life and

damage to property. There has been one documented dam failure in Sheridan County. In 1978 the

Reynolds #1 Dam partially failed. This earthen dam had its base keyed into the foundation. The breach

resulted from overtopping and subsequent erosion. There was no property damage or loss of life.

There have been no Presidential Declarations of a State of Emergency in Sheridan County as the result

of a dam failure. Additionally, there have been no state-level emergency declarations in Wyoming as

the result of a dam failure.15

14

The FEMA Flood Risk Report for Sheridan County referenced in this plan update was considered final on March 29, 2013. 15

State of Wyoming Multi-Hazard Mitigation Plan, Chapter 4 Dam Failure (http://wyohomelandsecurity.state.wy.us/mitigation_plan.aspx)

26

Impacts

Dam failure impacts documented in Sheridan County thus far have been minor. The City of Sheridan is

downstream of Twin Lakes No.1 (high hazard) and No. 2 (significant hazard) dams. Dams and reservoirs

serve a very important role for Wyoming residents and industry. Rarely, however, the dams fail, either

completely or partially, and become a significant hazard for those downstream.

Dam failures can be classified into four groups: overtopping, foundation failure, structural failure, and

other unforeseen failures. Hydraulic failures result from the uncontrolled flow of water over, around,

and adjacent to the dam. Earthen dams are most susceptible to this type of failure. Hydraulic failures

account for approximately 28% of all dam failures. Foundation and structural failures are usually tied to

seepage through the foundation of the main structure of the dam. Deformation of the foundation or

settling of the embankment can also result in dam failure. Structural failures account for approximately

28% of all dam failures, and foundation problems account for another 25%. Earthquakes or sabotage

account for 12% of all dam failures, while inadequate design and construction account for the remaining

7% of failures.

In 1981, the U.S. Army Corps of Engineers completed an inspection program for nonfederal dams under

the National Dam Inspection Act (P.L. 92-367). This was a four-year work effort and included compiling

an inventory of about 50,000 dams and conducting a review of each state’s capabilities, practices, and

regulations regarding design, construction, operation, and maintenance of dams. Part of the inspection

included evaluating the dams and assigning a hazard potential based on the effects downstream should

one of the dams fail. The dams were rated (1) high, (2) significant, and (3) low hazard. The Corps of

Engineers based the hazard potential designation on such items as acre-feet capacity of the dam,

distance from nearest community downstream, population density of the community, and age of the

dam. High hazard dam failures would involve property losses over $1 million and have probable loss of

life. There were 1,458 dams in Wyoming that were reviewed by the Corps of Engineers. Of that number

38 were rated high hazard, 56 were rated significant hazard, and the remaining 1,364 were rated low

hazard.

The Wyoming State Engineers Office (SEO) inspects dams over 20 feet high or with a storage capacity of

50 acre-feet or more, although smaller dams are also inspected in highly populated areas. In 2013, the

SEO reported that 1,516 dams where inspected once every five years by their office. Of those dams, 84

are rated high hazard, 104 were rated significant hazard, and 1,328 were rated low-hazard. Figure 2

shows the dams that are inspected by the Wyoming State Engineers Office. Sheridan County has 105

dams that are inspected by the Wyoming State Engineer’s Office. Eight are classified as having a high

hazard and five a significant hazard. The SEO Dam Safety Program has reported a reclamation trend and

decrease in dam renewals occurring in the Powder River Basin, which includes Sheridan County in 2013.

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Figure 2: Dams currently inspected by the Wyoming State Engineers Office, Dam Safety Program

Future Impacts

With thirteen high or significant dams within the County there is a possibility of dam failure flooding in

the future, with the potential for at least $1 million in flood damages and loss of life. Dams ranked high

or significant have inundation maps in the event of a dam failure. Because of Homeland Security

concerns, however, data on inundation areas remain unavailable for public consumption, making the

study and analysis of inundation areas for the purposes of publication within this plan non-productive.16

Development or future development along portions of Babione Creek, Coney Creek, Cross Creek Ditch,

East Fork Big Goose Creek, Five Mile Creek, North Fork Smith Creek, Prune Creek, Sawmill Creek, West

Fork Big Goose Creek, Wagner Draw and Windy Draw could be at risk to dam failure flooding. The

probability of dam failure is low.

Mitigation Strategy

The Sate Engineer is responsible for ensuring the safety and structural integrity of water storage facilities in the state. On-site inspections of facilities are made and any new or rehabilitation

16

State of Wyoming Multi-Hazard Mitigation Plan, Chapter 4 Dam Failure (http://wyohomelandsecurity.state.wy.us/mitigation_plan.aspx)

28

construction plans must be reviewed and approved by the State Engineer's Office. W.S 41-3-307 through 41-3-318.17

Proposed Sheridan County Mitigation Projects for Dam Failure Encourage residents, businesses and schools to purchase NOAA weather radios.

Public awareness program to include promotion of 72-hr kits and distribution of hazard information to residents and businesses via multiple media sources

Consider including Dam Failure Alerts in the Sheridan County Emergency Alert Procedures and Notification Exercises

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: High PROBABILITY: Low JURISDICTION AFFECTED: Sheridan, Dayton, Ranchester, portions of unincorporated County

17

Wyoming State Engineers Office, Safety of Dams Program

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Drought

Summary of Drought Section Update

• Expanded the History to include an drought risk outlook based on instrumentation record

• New Section for Mitigation Actions was added which identifies appropriate drought mitigation measures for Sheridan County

• Updated State of Wyoming Drought Category historic data table

• Updated Palmer Drought Severity Index (PDSI) 1895-2010

• Updated Surface Water Supply Index (SWSI) June 2013

• Updated Value of Crop and Livestock Production for the State of Wyoming and Production by Commodity for the State of Wyoming


Drought

Of all the natural weather-related disasters, drought is by far the most costly to our society. It indirectly kills more people and animals than the combined effects of hurricanes, floods, tornadoes, blizzards, and wildfires. And, unlike other disasters that quickly come and go, drought's long-term unrelenting destruction has been responsible in the past for mass migrations and lost civilizations. The 1980 and 1988 droughts in the US resulted in approximately 17,500 heat-related deaths and an economic cost of over $100 billion. Drought occurs in four stages and is defined as a function of its magnitude (dryness), duration, and regional extent. Severity, the most commonly used term for measuring drought, is a combination of magnitude and duration.

The first stage of drought is known as a meteorological drought. The conditions at this stage include any precipitation shortfall of 75% of normal for three months or longer. The second stage is known as agricultural drought. Soil moisture is deficient to the point where plants are stressed and biomass (yield) is reduced. The third stage is the hydrological drought. Reduced stream flow (inflow) to reservoirs and lakes is the most obvious sign that a serious drought is in progress. The fourth stage is the socioeconomic drought. This final stage refers to the situation that occurs when physical water shortage begins to affect people.

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As these stages evolve over time, the impacts to the economy, society, and environment converge into an emergency situation. Without reservoir water to irrigate farms, food supplies are in jeopardy. Without spring rains for the prairie grasslands, open range grazing is compromised. Without groundwater for municipalities, the hardships to communities result in increases in mental and physical stress as well as conflicts over the use of whatever limited water is available. Without water, wetlands disappear. The quality of any remaining water decreases due to its higher salinity concentration. There is also an increased risk of fires, and air quality degrades as a result of increased soil erosion in strong winds (blowing dust).

History and Outlook

The most recent statewide drought started in 1999, but began in earnest in the spring of 2000. It is considered by many to be the most severe in collective memory. However, some old timers have indicated that they remember streams drying up in the 1930s and 1950s. According to instrument records, since 1895 there have been only seven multi-year (three years or longer) statewide droughts. Based on deficit precipitation totals (negative departures from the long term average), they are ranked statewide. Figure 1 shows there was a temporary relief from drought conditions starting in 2008 and continuing into 2012.

Instrumentation Record

As a whole, Wyoming's precipitation record from 1895-2013 reveals that, for the first half of the 20th

century (except for the Dust Bowl years of the 1930s), there was generally a surplus of moisture. During

the second half of the century there was an increasing trend of increased periods of drought. Figure 1

presents the percentage of Wyoming experiencing a range of drought conditions by week spanning from

2000-2013. The most recent drought recorded can be noted by the dark red spikes starting in late 2000

and ending in early 2008. The State is again moving into drought conditions based on this figure in 2013.

Figure 2 supports the observations of Figure 1 but carried the record of observation back to 1895. The

same findings can be noted about the 2000-2008 extreme drought conditions. This report makes the

assumption that Sheridan County experiences similar normalized climatic conditions that are presented

in Figure 1 and 2 for the State of Wyoming.

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Figure 1: Drought Category by Week, Years 2000-201318

18

State of Wyoming Climate Office –Water Resource Data System

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Figure 2: Palmer Drought Severity Index (PDSI) 1895-201019

Palmer Drought Severity Index Classification System

-1.00 to 1.99 Mild drought

-2.00 to -2.99 Moderate drought

-3.00 to 3.99 Severe drought

-4.00 to -6.00 Extreme drought

19

National Oceanic Atmosphere Administration (NOAA)

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Based on the 2010-2013 drought condition climatic data presented in Figure 1 and the Surface Water

Supply Index (SWSI) for June 2013 presented in Figure 3 Sheridan County may be entering a period of

drought conditions. Figure 3 indicates that Sheridan County experienced a moderate drought conditions

in June 2013 and that conclusion is supported by the extreme drought conditions reported by the

Palmer Drought Severity Index in Figure 2.

Figure 3: Surface Water Supply Index (SWSI) June 201320

The Surface Water Supply Index (SWSI) is computed using only surface water supplies for the drainage. The

computation includes reservoir storage, if applicable, plus the forecast runoff. The index is purposely

created to resemble the Palmer Drought Index, with normal conditions centered near zero. Adequate and

excessive supply has a positive number and deficit water supply has a negative values. Soil moisture and

forecast precipitation are not considered as such, but the forecast runoff may consider these values.21

20 and 4

State of Wyoming Climate Office –Water Resource Data System http://www.wrds.uwyo.edu/wrds/nrcs/swsimap/swsimap.html

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Analysis and Impacts

Powder River at Arvada, July 11, 2002, 0 ft3/sec (mean = 316)22

The 1999-2003 drought can be shown to be the drought of historic record. There have been significant impacts on the agricultural industry from the 1999-2003 drought. The worst-case year was 2002, with a negative dollar impact of $308,171,390 statewide. Sheridan County is 2.6% of the State of Wyoming in land area. If it is assumed that the drought impact is equally distributed across the state, which in reality it is not, the potential drought impact in Sheridan County for 2002 would be approximately $8,000,000. The total impact statewide for the 1999-2003 drought is $565,489,036. If it is assumed that the drought impact is equally distributed across the state, which in reality it is not, the potential drought impact in Sheridan County would be approximately $14,700,000. Figure 1: Drought Category by Week for the State of Wyoming indicates that the State experienced a period of non-drought conditions from 2008-2012. Forecasting into 2013 and beyond indicates drought risk is indicated to increase and there is a potential negative impact on the agricultural industry in Sheridan County based on historical analysis listed above from the 2009 Sheridan County Multi-Hazard Mitigation Plan. Table 1 and Table 2 present the current value of Crop and Livestock Production and commodities in the State of Wyoming. If Wyoming continues to experience drought like conditions as described by Figures 1 and 2 the loss to the agricultural industry in Sheridan County will likely be greater than what was projected in the 2009 Sheridan County Multi-Hazard Mitigation Plan presented above.

22

D. Peterson, USGS (http://wy.water.usgs.gov/projects/drought/images/06317000_071102.jpg

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Table 1: Value of Crop and Livestock Production for the State of Wyoming23

23 Wyoming Agricultural Statistics 2013

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Table 2: Production by Commodity for the State of Wyoming24

24 Wyoming Agricultural Statistics 2013, http://www.nass.usda.gov/Statistics_by_State/Wyoming/Publications/Annual_Statistical_Bulletin/

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Proposed Sheridan County Mitigation Projects for Drought Education on xeriscaping for residential water conservation

Water conservation projects and studies

Enhanced forecasting and data distribution

Expanded or improved precipitation monitoring (Snowtel, etc.)

Explore local water restrictions

Seeking funding for outreach and implementation of more efficient agriculture irrigation systems

Summary

PROPERTY AFFECTED: High POPULATION AFFECTED: High PROBABILITY: Medium JURISDICTION AFFECTED: County

Drought Links

Percentage of Wyoming in Each Drought Category from 01-Jan-2000 to present Wyoming's Drought Plan (PDF) U.S. Drought Monitor National Integrated Drought Information System Drought Monitoring Products NOAA's Drought Information Center USGS Wyoming Drought Watch

http://www.wrds.uwyo.edu/sco/drought/droughttimeline.html

http://www.wrds.uwyo.edu/sco/drought/droughtplan.pdf

http://drought.unl.edu/MonitoringTools/USDroughtMonitor.aspx

http://www.drought.gov/portal/server.pt

http://www.wrds.uwyo.edu/sco/drought/wy_drought_2001/wy_drought.html

http://www.drought.noaa.gov/

http://wy.water.usgs.gov/projects/drought/index.html

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Earthquake

Summary of Earthquake Section Update

• According the Wyoming Geological Survey Hazard Section, no new and/or updated maps or hazard data for Sheridan County was available at the time of this update.

• New Section for Mitigation Actions was added which identifies appropriate Earthquake mitigation measures for Sheridan County.


Earthquake

An earthquake is generally defined as a sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain. The most common types of earthquakes are caused by movements along faults and by volcanic forces, although they can also result from explosions, cavern collapse, and other minor causes not related to slowly accumulated strains.

History

Historically, earthquakes have occurred in every county in Wyoming (Figure 1). The first was reported in Yellowstone National Park in 1871. Yellowstone National Park is one of the more seismically active areas in the United States.

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Figure 1: Historic Earthquakes in Wyoming

Historic Seismicity in Sheridan County Four magnitude 3.0 or intensity III and greater earthquakes have been recorded in Sheridan County. These earthquakes are discussed below. Only one earthquake occurred in Sheridan County during the 1920s. On January 17, 1923, an intensity III earthquake occurred 6.5 miles southwest of Sheridan. No damage was reported from this event. Sheridan County did not experience another earthquake until the mid-1900s. On April 26, 1953, an intensity IV earthquake was reported approximately 3 miles east-northeast of Sheridan. Area residents reported that some beds were rocked, dishes were rattled, and some electrical wires swayed (Murphy and Cloud, 1955). On November 23, 1973, an earthquake was reported approximately 2.5 miles east of Dayton. This event was later determined to be the result of a probable explosion in the area. A magnitude 3.6, intensity IV

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earthquake was reported on March 24, 1977, approximately 6 miles south-southwest of Big Horn. No damage was associated with this event. Most recently, a 3.9 magnitude earthquake occurred in northeastern Sheridan County on February 25, 1993. This earthquake was centered approximately 19 miles north-northeast of Arvada. No damage was reported.

Regional Historic Seismicity Several earthquakes have also occurred near Sheridan County. The first took place in Johnson County on October 24, 1922, approximately 28 miles southwest of Clearmont. The Sheridan Post reported that at Cat Creek, eight miles east of Sheridan, homes were shaken and dishes rattled. This intensity IV-V earthquake was only slightly felt in the town of Sheridan. On November 17, 1925, an intensity V event occurred in southeastern Big Horn County, approximately 33 miles southwest of Story. People in Sheridan, Fort McKenzie, and at Dome Lake Resort in the Big Horn Mountains reported feeling the earthquake tremors. The tremors shook cabins, pictures, and furniture. A “distinct roar” heard at Dome Lake was attributed to a possible earthquake-induced landslide (Casper Daily Tribune, November 18,1925). One day later, on November 18,1925, people in the Dome Lake area reported feeling another tremor (Sheridan Post-Enterprise, November 19, 1925). No damage was reported from either event.

An intensity IV earthquake was felt in the Sheridan area on September 6, 1943, causing beds and chairs

“to sway” (Casper Tribune-Herald, September 7, 1943). The epicenter of this earthquake was later found

to be near Buffalo, approximately 21 miles south-southeast of Story (Reagor, Stover, and Algermissen,

1985).

On September 2, 1962, an earthquake was recorded in Big Horn County, approximately 12.5 miles south-southwest of Burgess Junction. No one reported damage or feeling this event. (U.S.G.S. National Earthquake Information Center). Two earthquakes were recorded near Sheridan County in 1976. On August 8, 1976, a magnitude 3.4 earthquake occurred in southern Montana, approximately 25 miles northeast of Sheridan. A few months later, on October 8, 1976, a magnitude 3.5 earthquake was detected in the same area. According to the U.S.G.S. National Earthquake Information Center, no one reported feeling either event. A magnitude 5.1, intensity V earthquake occurred in Johnson County on September 7, 1984, approximately 32 miles southeast of Clearmont. The earthquake was felt throughout northeastern Wyoming, including Buffalo, Casper, Kaycee, Linch, and Midwest, and in parts of southeastern Montana. No significant damage was reported (Laramie Daily Boomerang, September 8, 1984). On February 22, 1992, a magnitude 2.9 event was recorded approximately 22 miles south-southeast of Clearmont. No damage was reported from this earthquake. Most recently, an earthquake was reported in eastern Big Horn County on February 12, 1998, approximately 35 miles southwest of Big Horn. No one reported feeling this magnitude 3.0 event (U.S.G.S. National Earthquake Information Center).

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Deterministic Analysis of Regional Active Faults with a Surficial Expression

There are no known exposed active faults with a surficial expression in Sheridan County. As a result, no fault-specific analysis can be generated for Sheridan County.

Floating or Random Earthquake Sources Many federal regulations require an analysis of the earthquake potential in areas where active faults are not exposed, and where earthquakes are tied to buried faults with no surface expression. Regions with a uniform potential for the occurrence of such earthquakes are called tectonic provinces. Within a tectonic province, earthquakes associated with buried faults are assumed to occur randomly, and as a result can theoretically occur anywhere within that area of uniform earthquake potential. In reality, that random distribution may not be the case, as all earthquakes are associated with specific faults. If all buried faults have not been identified, however, the distribution has to be considered random. “Floating earthquakes” are earthquakes that are considered to occur randomly in a tectonic province. It is difficult to accurately define tectonic provinces when there is a limited historic earthquake record. When there are no nearby seismic stations that can detect small-magnitude earthquakes, which occur more frequently than larger events, the problem is compounded. Under these conditions, it is common to delineate larger, rather than smaller, tectonic provinces. The U.S. Geological Survey identified tectonic provinces in a report titled “Probabilistic Estimates of Maximum Acceleration and Velocity in Rock in the Contiguous United States” (Algermissen and others, 1982). In that report, Sheridan County was classified as being in a tectonic province with a “floating earthquake” maximum magnitude of 6.1. Geomatrix (1988b) suggested using a more extensive regional tectonic province, called the “Wyoming Foreland Structural Province”, which is approximately defined

by the Idaho-Wyoming Thrust Belt on the west, 104 West longitude on the east, 40 North latitude on

the south, and 45 North latitude on the north. Geomatrix (1988b) estimated that the largest “floating” earthquake in the “Wyoming Foreland Structural Province” would have a magnitude in the 6.0 – 6.5 range, with an average value of magnitude 6.25. Federal or state regulations usually specify if a “floating earthquake” or tectonic province analysis is required for a facility. Usually, those regulations also specify at what distance a floating earthquake is to be placed from a facility. For example, for uranium mill tailings sites, the Nuclear Regulatory Commission requires that a floating earthquake be placed 15 kilometers from the site. That earthquake is then used to determine what horizontal accelerations may occur at the site. A magnitude 6.25 “floating” earthquake, placed 15 kilometers from any structure in Sheridan County, would generate horizontal accelerations of approximately 15%g at the site. That acceleration would be adequate for designing a uranium mill tailings site, but may be too large for less critical sites, such as a landfill. Critical facilities, such as dams, usually require a more detailed probabilistic analysis of random earthquakes. Based upon probabilistic analyses of random earthquakes in an area distant from exposed active faults (Geomatrix, 1988b), however, placing a magnitude 6.25 earthquake at 15 kilometers from a site will provide a fairly conservative estimate of design ground accelerations.

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Probabilistic Seismic Hazard Analyses

The U.S. Geological Survey (USGS) publishes probabilistic acceleration maps for 500-, 1000-, and 2,500-year time frames. The maps show what accelerations may be met or exceeded in those time frames by expressing the probability that the accelerations will be met or exceeded in a shorter time frame. For example, a 10% probability that acceleration may be met or exceeded in 50 years is roughly equivalent to a 100% probability of exceedance in 500 years. The USGS has recently generated new probabilistic acceleration maps for Wyoming (Case, 2000). Copies of the 500-year (10% probability of exceedance in 50 years), 1000-year (5% probability of exceedance in 50 years), and 2,500-year (2% probability of exceedance in 50 years) maps are attached. Until recently, the 500-year map was often used for planning purposes for average structures, and was the basis of the most current Uniform Building Code. The new International Building Code, however, uses a 2,500-year map as the basis for building design. The maps reflect current perceptions on seismicity in Wyoming. In many areas of Wyoming, ground accelerations shown on the USGS maps can be increased due to local soil conditions. For example, if fairly soft, saturated sediments are present at the surface, and seismic waves are passed through them, surface ground accelerations will usually be greater than would be experienced if only bedrock was present. In this case, the ground accelerations shown on the USGS maps would underestimate the local hazard, as they are based upon accelerations that would be expected if firm soil or rock were present at the surface. Intensity values can be found in Table 1 with an expanded definition of intensity values in Table 2. Based upon the 500-year map (10% probability of exceedance in 50 years) (Figure 2), the estimated peak horizontal acceleration in Sheridan County ranges from 3%g in the northern portion of the county to over 5%g in the southern portion of the county. These accelerations are roughly comparable to intensity IV earthquakes (1.4%g – 3.9%g) to intensity V earthquakes (3.9%g - 9.2%g). Intensity IV earthquakes cause little damage. Intensity V earthquakes can result in cracked plaster and broken dishes. Sheridan would be subjected to an acceleration of approximately 4-5%g or intensity V. Based upon the 1000-year map (5% probability of exceedance in 50 years) (Figure 3), the estimated peak horizontal acceleration in Sheridan County ranges from 5%g in the northwestern part of the county to over 9%g in the southeastern portion of the county. These accelerations are roughly comparable to intensity V earthquakes (3.9%g – 9.2%g). Intensity V earthquakes can result in cracked plaster and broken dishes. Sheridan would be subjected to an acceleration of approximately 7 - 8%g or intensity V. Based upon the 2500-year map (2% probability of exceedance in 50 years) (Figure 4), the estimated peak horizontal acceleration in Sheridan County ranges from 9%g in the northwestern corner of the county to nearly 19%g in the southeastern corner of the county. These accelerations are roughly comparable to intensity V earthquakes (3.9%g – 9.2%g), intensity VI earthquakes (9.2%g – 18.0%g), and intensity VII earthquakes (18%g – 34%g). Intensity V earthquakes can result in cracked plaster and broken dishes. Intensity VI earthquakes can result in some heavy furniture can be moved. There may be some instances of fallen plaster and damaged chimneys. Intensity VII earthquakes can result in slight to moderate damage in well-built ordinary structures and considerable damage in poorly built or badly designed structures, such as unreinforced masonry. Chimneys may be broken. Sheridan would be subjected to an acceleration of nearly 14%g or intensity VI. As the historic record is limited, it is nearly impossible to determine when a 2,500-year event last occurred in the county. Because of the uncertainty involved, and based upon the fact that the new

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International Building Code utilizes 2,500-year events for building design, it is suggested that the 2,500-year probabilistic maps be used for Sheridan County analyses. This conservative approach is in the interest of public safety. Table 1: Abridged Modified Mercalli Intensity Scale

Modified Mercalli Intensity

Acceleration (%g)

(PGA)

Perceived Shaking

Potential Damage

I <0.17 Not felt None

II 0.17 – 1.4 Weak None

III 0.17 – 1.4 Weak None

IV 1.4 – 3.9 Light None

V 3.9 – 9.2 Moderate Very Light

VI 9.2 – 18 Strong Light

VII 18 – 34 Very Strong Moderate

VIII 34 – 65 Severe Moderate to Heavy

IX 65 – 124 Violent Heavy

X >124 Extreme Very Heavy

XI >124 Extreme Very Heavy

XII >124 Extreme Very Heavy

Modified Mercalli Intensity and peak ground acceleration (PGA) (Wald, et al 1999).

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Table 2: Modified Mercalli Intensity Scale value and description

I Not felt except by a very few under especially favorable circumstances.

II Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.

III Felt quite noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing automobiles may rock slightly. Vibration like passing of truck. Duration estimated.

IV During the day felt indoors by many, outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make creaking sound. Sensation like heavy truck striking building. Standing automobiles rocked noticeably.

V Felt by nearly everyone, many awakened. Some dishes, windows, and so on broken; cracked plaster in a few places; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.

VI Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster and damaged chimneys. Damage slight.

VII Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving cars.

VIII Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving cars disturbed.

IX Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken.

X Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed, slopped over banks.

XI Few, if any, (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.

XII Damage total. Waves seen on ground surface. Lines of sight and level distorted. Objects thrown into the air.

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Figure 2: 500-year probabilistic acceleration map (10% probability of exceedance in 50 years)

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Figure 3: 1,000-year probabilistic acceleration map (5% probability of exceedance in 50 years)

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Figure 4: 2,500-year probabilistic acceleration map (2% probability of exceedance in 50 years)

Impacts

There have been fourteen historic magnitude 3.0 or intensity III and greater earthquakes recorded in or near Sheridan County. Because of the limited historic record, it is possible to underestimate the seismic hazard in Sheridan County if historic earthquakes are used as the sole basis for analysis. Earthquake and ground motion probability maps give a more reasonable estimate of damage potential in areas without exposed active faults at the surface, such as Sheridan County. Current earthquake probability maps that are used in the newest building codes suggest a scenario that would result in moderate damage to buildings and their contents, with damage increasing from the

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northwest to the southeast. More specifically, the probability-based worst-case scenario could result in the following damage at points throughout the county: In intensity VII earthquakes, damage is negligible in buildings of good design and construction, slight-to-moderate in well-built ordinary structures, considerable in poorly built or badly designed structures such as unreinforced masonry buildings. Some chimneys will be broken.

Intensity VII Earthquake Areas

Ucrosse

In intensity VI earthquakes, some heavy furniture can be moved. There may be some instances of fallen plaster and damaged chimneys.

Intensity VI Earthquake Areas

Acme

Arvada

Banner

Beckton

Bighorn

Burgess Junction

Clearmont

Dayton

Leiter

Parkman

Ranchester

Sheridan

Story

Potential Future Damage Impacts HAZUS (Hazards U.S.) is a nationally standardized, GIS-based, risk assessment and loss estimation computer program that was originally designed in 1997 to provide the user with an estimate of the type, extent, and cost of damages and losses that may occur during and following an earthquake. It was developed for the FEMA by the National Institute of Building Sciences (NIBS). There have been a number of versions of HAZUS generated by FEMA, with HAZUS-MH (HAZUS – Multi-Hazard) being the most recent release. HAZUS-MH incorporates a flood and wind module with the previously existing earthquake module. Hazus-99 (1999 version) was previously used by the Wyoming State Geological Survey (WSGS).

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HAZUS was originally designed to generate damage assessments and associated ground motions based largely upon analysis at the census-tract level. Census tracts average 4,000 inhabitants, with the tract boundaries usually representing visible features. HAZUS-99 calculated a ground motion value for the centroid of a census tract, and applied that value to the entire tract. The calculations are based on United States Geological Survey National Seismic Hazard Maps. In many of the western states, census tracts are very large, and parts of the tracts may be subjected to ground shaking that is considerably different than the value at the centroid. FEMA Region VIII and their subcontractor on HAZUS, PBS&J from Atlanta, have worked closely with the Wyoming State Geological Survey (WSGS) to develop a census-block-based analysis for HAZUS-MH in Wyoming. In fact, Wyoming is the national pilot project for the census-block-based analysis. The block-level analysis is a significant improvement. Census blocks are a subdivision of census tracts. Many blocks correspond to individual city blocks bounded by streets, but blocks – especially in rural areas – may include many square miles and may have some boundaries that are not streets. Ground motion values for Wyoming are now calculated at the centroid of census blocks.

As part of the development of the State of Wyoming Multi-Hazard Mitigation Plan a HAZUS probabilistic

scenario was run for every Wyoming County. The scenario used a 2,500 year return period, and uses the

USGS ground shaking data represented in figure 5.4. The probability of such an event is 2% in 50 years.

Sheridan County used a driving Magnitude of 6.5 associated with the scenario. The results are presented

in Tables 2 through 4.

There are two methods to rank the counties to determine where earthquake impacts may be the greatest. Either the loss ratios (Table 5.3) or total damage (Table 5.4) figures can be used. The loss ratio is determined by dividing the sum of the structural and non-structural damage by the total building value for the county. The loss ratio is a better measure of impact for a county as it gives an indication of the percent of damage to buildings. The total damage figure by itself does not reflect the percentage of building damage. If a county has a number of valuable buildings, such as Laramie County, small damage to a number of valuable buildings may result in a higher total damage figure that may be found in a county with fewer, less expensive buildings, with a higher percentage of damage.

Table 2: HAZUS Probabilistic Scenario for Sheridan County

County Capital Stock Losses

(Thousands of Dollars)

Loss Ratio (%)

Income Losses (Thousands of Dollars)

Total Loss (Thousands of

Dollars)

Structural

Non-structural

Contents Inventory

Relocation

Capital-Related

Wages Rental Loss

Sheridan 7,830 29,154 12,057 $233 2.09 213 1,898 2,402 2,636 56,423

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Table 3: County Impacts Rated by Loss Ratio

County Loss Ratio

Total Loss (Thousands of Dollars)

Lincoln 31.08 391,727

Teton 24.72 681,981

Uinta 15.84 241,284

Sublette 8.24 58,340

Hot Springs 4.20 21,136

Converse 4.15 44,482

Natrona 3.99 268,911

Fremont 3.75 53,860

Washakie 3.54 26,925

Johnson 3.40 24,320

Carbon 3.08 37,762

Park 2.98 86,004

Sweetwater 2.84 93,017

Big Horn 2.43 22,660

Albany 2.32 71,078

Sheridan 2.09 56,423

Platte 1.60 12,850

Campbell 1.37 40,144

Laramie 1.25 92,963

Niobrara 1.20 2,935

Goshen 1.13 13,364

Crook 1.04 4,867

Weston 0.96 5,760

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Table 4: County Impacts Rated by Dollar Loss

County Total Loss (Thousands of Dollars)

Loss Ratio

Teton 681,981 24.72

Lincoln 391,727 31.08

Natrona 268,911 3.99

Uinta 241,284 15.84

Sweetwater 93,017 2.84

Laramie 92,963 1.25

Park 86,004 2.98

Albany 71,078 2.32

Sublette 58,340 8.24

Sheridan 56,423 2.09

Fremont 53,860 3.75

Converse 44,482 4.15

Campbell 40,144 1.37

Carbon 37,762 3.08

Washakie 26,925 3.54

Johnson 24,320 3.4

Big Horn 22,660 2.43

Hot Springs 21,136 4.2

Goshen 13,364 1.13

Platte 12,850 1.6

Weston 5,760 0.96

Crook 4,867 1.04

Niobrara 2,935 1.2

In summary, it is estimated that if a worse case event occurred in Sheridan County, $56 million in building related damage could occur. HAZUS estimates that 867 buildings (8.7% of the total in the County), would be at least moderately damaged. The probability of such an event is 2% in 50 years.

Proposed Sheridan County Mitigation Projects for Earthquakes

Encourage residents, businesses and schools to purchase NOAA weather radios.

Public awareness program to include promotion of 72-hr kits and distribution of hazard information to residents and businesses via multiple media sources

Encourage people to make informed decisions about purchase of earthquake/ground movement insurance

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Summary PROPERTY AFFECTED: Low POPULATION AFFECTED: Medium PROBABILITY: Low JURISDICTION AFFECTED: County Reference: Basic Seismological Characterization for Sheridan County, Wyoming by James C. Case, Rachel N. Toner, and Robert Kirkwood Wyoming State Geological Survey September 2002 http://www.wrds.uwyo.edu/wrds/wsgs/hazards/quakes/seischar/seischar.html

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Flood and Ice Jamming

Summary of Flood and Ice Jamming Section Update

Expansion of definition of 'Flood' to include factors that contribute to flood risks

New National Flood Insurance section which includes details regarding Sheridan County's participation in the Community Rating System, Past NFIP Claims and Loss Statistics, and FEMA Flood Assistance Programs and Projects

New section that address FEMA Map Modernization Program and Risk MAP activities in Sheridan County

Updated Flood History Table 1923-2012 for Sheridan County and Jurisdictions

Updated Flood Risk Assessment which includes comparison of older FIRMs to the new DFIRM, new HAZUS-MH Flood Building Exposure and Loss Estimates for Sheridan County, Town of Ranchester, Town of Dayton, and Town of Clearmont

New Section on Ice Jamming in Sheridan County which includes a Historic Table of reported Ice Jams for Sheridan County from 1922-2009

New Section on the Sheridan County Flood Mitigation Strategy which includes Mitigation Successes in Sheridan County and Participating Jurisdictions and an overview of Types of Mitigation Actions.

New Section on Flood Mitigation Programs and Assistance

New Mitigation Action Breakout section about the NOAA Stream Gage System in Sheridan County

New Proposed Sheridan County Mitigation Projects for Flooding and Ica Jamming

Flood Overview A flood is an accumulation of water over normally dry areas. A flood, as defined by the National Flood Insurance Program (NFIP), is a general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties from: overflow of waters; unusual and rapid accumulation or runoff of surface waters from any source; or, a mudflow. Floods can be slow or fast rising, but generally develop over a period of many hours or days. Floods have been a significant problem in Sheridan County.

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Floods can also occur with little or no warning and can reach full peak in only a few minutes. Such floods are called flash floods. A flash flood usually results from intense storms dropping large amounts of rain within a brief period. Floods can occur for reasons other than precipitation or rapidly melting snow. They can also occur because of ice jams. Sheridan County has experienced many flooding events and has taken significant flood mitigation actions to decrease the impacts of flooding and reduce the potential impacts to Sheridan County residents and property.

Floods become hazards to people and property by inundating developed areas. Flood losses range from damage to landscaping and debris generation to building damage and injury or death. The following factors contribute to flood risk:

Probability, or likelihood, is a calculation of the chance of different size floods occurring.

Impacts of a flood are the consequences related to human activities and how floods can change the natural and built environments.

Vulnerabilities in a community are the structures and population subject to flooding that may experience negative impacts because of location, age, or other characteristics.

Sources of flooding in Sheridan County include the Powder River, Tongue River, Big Goose Creek, the Little Goose Creek, Clear Creek, Prairie Dog Creek, Piney Creek, and other small creeks, washes and drainages.

The following sections will present a summary of flood hazard risk information and analysis that can be found in the Sheridan County FEMA Flood Insurance Study25, Flood Risk Report26, the 2009 Sheridan County Multi-Hazard Mitigation Plan and 2010 State of Wyoming Multi-Hazard Mitigation plan27.

National Flood Insurance Program (NFIP)

Congress created the National Flood Insurance Program (NFIP) in 1968 to help provide a means for property owners to financially protect themselves. The NFIP offers flood insurance to homeowners, renters, and business owners if their community participates in the NFIP. Participating communities agree to adopt and enforce ordinances that meet or exceed FEMA requirements to reduce the risk of flooding28.

According to the National Flood Insurance Program’s Community Status Book29 Sheridan County has been mapped for flood hazards and participates in the NFIP. The incorporated communities of the City

25

The FEMA Flood Insurance Study (FIS) for Sheridan County was considered preliminary at the time of this plan update. The participating NFIP communities in Sheridan County where in the process of final adoption so information referenced in the Sheridan County FIS is considered relevant and final. 26

The FEMA Flood Risk Report for Sheridan County referenced in this plan update was considered final on March

29, 2013. All narrative, data, and mapping products presented in the FEMA Risk Report for Sheridan County was considered final at the time of this plan update. 27

State of Wyoming Multi-Hazard Mitigation Plan, Chapter 8 Flood (http://wyohomelandsecurity.state.wy.us/mitigation_plan.aspx) 28

http://www.fema.gov/national-flood-insurance-program 29

http://www.fema.gov/national-flood-insurance-program/national-flood-insurance-program-community-status-book

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of Sheridan, Town of Clearmont, Town of Dayton, and Town of Ranchester also have been mapped and participate in the NFIP. Details of participation and map status are shown in table 1 below. At the time of this plan update Sheridan County and participating jurisdictions were in the process of adopting the final Digital Flood Insurance Rate Maps (DFIRMs) and Flood Insurance Study (FIS). Final adoption of DFIRMs is scheduled for January 2014.

Table 1: NFIP Community Status Book Results as of September 2013

CID Community Name County Initial FHBM

Identified Initial FIRM Identified

Current Effective Map

Date

Currently participating in the NFIP

560045 Town of Dayton Sheridan 9/6/1974 8/1/2008 8/1/2008 Yes

560046 Town of

Ranchester Sheridan 9/6/1974 04/15/1988 01/20/1999 Yes

560047 Sheridan County Sheridan 7/4/1978 08/01/1986 03/30/1998 Yes

560044 City of Sheridan Sheridan 1/16/1974 09/01/1978 01/19/2001 Yes

560107 Town of Clearmont Sheridan 1/16/2014 1/16/14 Yes

Sheridan County, the City of Sheridan, Town of Dayton, and Town of Ranchester currently participate in the National Flood Insurance Program and are committed to continued compliance with the requirements of the NFIP. At the time of this plan update the Town of Clearmont was not participating in the NFIP but efforts to encourage participation have been made and will continue in the future.

Community Rating System (CRS)

The NFIP’s CRS is a voluntary incentive program that recognizes and encourages community floodplain management activities that exceed the minimum NFIP requirements. As a result, flood insurance premium rates are discounted to reflect the reduced flood risk resulting from community actions meeting the three goals of the CRS: to reduce flood losses, to facilitate accurate insurance rating, and to promote the awareness of flood insurance.

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For CRS participating communities, flood insurance premium rates are discounted in increments of 5%; i.e., a Class 1 community would receive a 45% premium discount, while a Class 9 community would receive a 5% discount. (A Class 10 is not participating in the CRS and receives no discount.) The City of Sheridan has participated in the Community Rating System (CRS) since 1995 and is a Class 9 Community. The CRS is a voluntary program for NFIP participating communities to further reduce flood damage in exchange for discounted insurance premiums.

Past NFIP Claims

There are 254 NFIP policies in Sheridan County, and there have been 43 NFIP insurance claims (3 in Ranchester, 22 in Sheridan, 18 in unincorporated areas of the county). Table 2 presents the NFIP Loss Statistics available through June 30, 2013. There are no repetitive loss structures in Sheridan County.

Table 2: NFIP Loss Statistics January 1, 1978 through June 30, 201330

County Name Community Name Total

Losses Closed Losses

Open Losses

CWOP Losses

Payments

Sheridan RANCHESTER, TOWN OF 4 3 0 1 $21,461.94

Sheridan SHERIDAN COUNTY * 22 8 1 13 $27,041.24

Sheridan SHERIDAN, CITY OF 21 10 1 10 $19,894.69

Additional Flood Assistance Programs and Projects

FEMA’s Public Assistance Program provides aid in the wake of a major disaster to state and local governments and to certain non‐profits, to help communities in their recovery efforts. Public Assistance claim locations may indicate areas where high flood insurance coverage or other mitigation actions are needed. There have been 23 Public Assistance projects in Sheridan County, which include the following types of work: 2 debris removal, 5 protective services, 8 roads and bridges, 1 recreation or other, 6 fire management, and 1 state management. FEMA’s Individual Assistance Program provides money or direct assistance to individuals whose property has been damaged and destroyed as a result of a federally‐declared disaster and whose losses are not covered by insurance. At the time of this plan update, there has not been a past disaster declaration in Sheridan County resulting in the availability of Individual Assistance. Figure 1 presents the spatial distribution of current NFIP policy locations, FEMA Public Assistance Projects and the number of insurance claims that have been made in Sheridan County.

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http://bsa.nfipstat.fema.gov/reports/1040.htm#56

http://bsa.nfipstat.fema.gov/reports/1040.htm#56

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Figure 1: Sheridan County NFIP Policies and Claims and Public Assistance Projects

FEMA’s Map Modernization Program and transition to RISK MAP in Sheridan County

The Federal Emergency Management Agency (FEMA) Flood Map Modernization program was a multiyear Presidential initiative started in 2003 that was directed at improving and updating the Nation’s flood hazard identification maps. In 2010 FEMA started transitioning into a new revised approach called Risk Mapping, Assessment, and Planning (Risk MAP). The vision for Risk MAP is to deliver quality data that increases public awareness and leads to action that reduces risk to life and property. Risk MAP builds on flood hazard data and maps produced during the Flood Map Modernization program. Risk MAP is currently focused on providing communities with flood information and tools which can be used to enhance local mitigation plans and take action to better protect citizens. Through more precise flood mapping products, risk assessment tools, and planning and outreach support, Risk MAP strengthens local ability to make informed decisions about reducing risk. By pairing accurate floodplain maps with risk assessment tools and planning and outreach support, Risk MAP has transformed traditional flood mapping efforts into an integrated process of identifying, assessing, communicating, planning for, and mitigating flood-related risks.

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For the state of Wyoming, there have not been any full fledge RiskMAP projects, but there have been two counties that were started during the Map Modernization period and converted into RiskMAP project. Sheridan County is one of those counties. FEMA produced new preliminary floodplain maps for Sheridan County in 2012, and then in 2013, the communities also received a Flood Risk Report and Flood Risk Database. The goal of the Flood Risk Report and Flood Risk Database is to help inform and enable communities to take action to reduce flood risk.

Through the Risk MAP program, FEMA provides communities with updated digital Flood Insurance Rate Maps (FIRMs) and Flood Insurance Studies (FISs) that describe the probability of floods and show flood boundaries and elevations. FEMA also provides the following flood risk products:

Flood Risk Report: Presents key risk analysis data for the project area and discusses areas of mitigation interest.

Flood Risk Database: Contains flood risk data as a Geographic Information Systems (GIS) geodatabase to be used and updated by the community.

The Flood Risk Database and Flood Risk Report are “non‐regulatory” products. They are available and intended for community use, but are neither mandatory nor tied to the regulatory floodplain management and insurance requirements of the National Flood Insurance Program (NFIP). They may be used as regulatory products by communities if authorized by State and local enabling authorities.

Flood History

The documented flood history for Sheridan County extends back to 1923. On September 23, 1923 an overabundance of rain caused flooding resulting in wooden paving blocks washed downstream, flooded basements, and flooded bridges. Accumulated debris under bridges caused water to backup. The amount of damage was estimated at $500,000. The Powder River at Arvada had a peak discharge of 100,000 CFS.

The abbreviated flood history was in large part derived from the monthly Storm Data reports generated and released by the National Oceanic and Atmospheric Administration’s National Climate Center. Other sources are unpublished reports from the Wyoming Office of Homeland Security, newspaper accounts, and periodicals from public libraries. Table 3 presents flooding events that have caused damage, injuries, or loss of life in Sheridan County. A damaging flood occurs in the County every five years on average, based upon the historical data. The data indicates that the majority of floods occur in May and June, when snow-melt runoff is augmented by heavy rain.

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Table 3: Sheridan County Flood History Data 1923-2012

County Location Start/End Date Deaths Injuries Property Damage

Crop Damage

Total Damage

Information

Sheridan

Sheridan, Big Goose Creek, Little Goose

Creek

September 29, 1923

$500,000 $500,000

An overabundance of rain caused flooding resulting in wooden paving blocks washed downstream, flooded basements, and flooded bridges. Also, accumulated debris under bridge caused water backup; amount of damage estimated at $500,000. Powder River at Arvada had a discharge of 100,000 CFS.

Sheridan May 1, 1938 Heavy snows in Sheridan County caused local damaging floods during the latter part of the month.

Sheridan Northeast

portion of the state

January 1, 1943

Chinook conditions over the northeast portion of the State caused rapid melting of the snow, and as a result, serious floods occurred. The town of Gillette was especially hard hit by a flood on the 22nd. Reports from the Big Horn Basin state that the ice in the river went out on the 22nd causing serious floods to farms near the river.

Sheridan

Sheridan, Little Goose Creek,

Big Goose Creek

June 3, 1944

A 15-year flood from an overabundance of rain resulted in flooded basements and bridges. According to WEMA Flood Damage Inventory the Tongue River near Dayton had a discharge of 3400 CFS and according to FEMA Flood Insurance Study January 19, 2001 it had a discharge of 4040 CFS.

Sheridan Arvada June 14, 1953

A flash flood near Arvada on the Lower Crazy Woman Creek on the 14th followed a rain and hailstorm. There was some damage to roads and meadows which was largely counter-balanced by the beneficial effects of the moisture.

Sheridan Sheridan,

Prairie Dog Creek

June 27, 1953 Heavy rain (3.4 inches in one hour) caused flooding, damaging ranches and loss of equipment.

Sheridan Northeast Wyoming

August 2, 1953 $50,000 $1,000 $51,000 A heavy rain the afternoon of the 2nd caused flood and property damage in northeastern Wyoming estimated at $50,000 and crop damage of $1,000.

Sheridan Clearmont 5 SW September 4,

1954 $1,000 $1,000

An intense hailstorm at Clearmont 5 SW, during the evening of the 4th, caused flood damage of about $1000 to reservoirs and irrigation ditches.

Sheridan

Sheridan, Big Goose Creek, Little Goose

Creek

0/00/1956 A less than 10-year flood caused by heavy rain flooded basements and destroyed crops and gardens. Discharge amount was 3360 CFS.

Sheridan Ranchester June 2, 1957

A deluge at Ranchester northwest of Sheridan on the 2nd caused flooding by small creeks and irrigation ditches. Power and telephone lines were damaged by lightning. An unofficial measurement of rainfall indicated over three inches of rain in one hour.

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Crop Damage

Total Damage

Information

Sheridan Sheridan June 15, 1962 $22,500 $22,500 Heavy thundershowers caused flash flooding in Sheridan area.

Sheridan Sheridan June 29, 1962 $22,500 $22,500 Flash flooding from heavy rains occurred in Sheridan area.

Sheridan Arvada July 12, 1962 $22,500 $22,500 Heavy rains on both afternoons caused flash flooding with damage to crops, reservoirs, and roads in the Arvada vicinity.

Park, Sheridan, Big

Horn, Washakie,

Hot Springs and Fremont

June 15, 1963 0 0 $2,250,000 $0 $2,250,000

Heavy rains in the Wind River, Absaroka, and Big Horn Mountains caused flash flooding during Saturday and Sunday, the 15th and 16th. Considerable damage done to homes, equipment, crops, irrigation canals, roads and bridges.

Sheridan Sheridan,

Goose Creek, Clear Creek

June 15-16, 1963 1 0 $0 $0 $0

Heavy rains combined with snowmelt runoff, including a storm sewer backing up, caused flooding, resulting in damage to basements and US Army Corps of Engineers Flood Protection project. There was 1 death in Sheridan according to the Wyoming Floods and Droughts, National Weather Summary 1988-90. The following are discharge values from WEMA Storm Data: South Piney Creek near Story (June 15) - 2090 CFS, North Piney Creek near Story (June 15) - 1820 CFS, Piney Creek at Ucross (June 16) - 3570 CFS, East Goose Creek near Big Horn (June 16) - 1230 CFS, Middle Fork Powder River near Barnum (June 16) - 7110 CFS, Largest recorded at Sheridan Gauge (June 16) - 5450 CFS. According to WEMA Storm Data and Flood Damage Inventory it was a 45-year flood and according to Wyoming Floods and Droughts, National Weather Summary 1988-90 it was a 20- to greater than 100-year flood.

Sheridan Sheridan June 20, 1975 0 0 $225,000 $0 $225,000

Heaviest rainfall was in the city of Sheridan. 2.51 inches of rain - the second greatest 24-hour amount recorded for June - fell at the Sheridan Airport between 11:00 p.m. on the 20th and 1100 MST on the 21st. Many basements were flooded in the city of Sheridan.

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Crop Damage

Total Damage

Information

Park, Big Horn,

Campbell, Converse,

Crook, Johnson, Natrona, Sheridan, Washakie,

Weston, Hot Springs, and

Niobrara

Central and North portions

of Wyoming May 15, 1978 0 0 $15,500,000 $0 $15,500,000

Heavy wet snow and record rains did very extensive damage to property, crops, and livestock in 12 counties. Hundreds of homes were damaged, and many totally destroyed. Numerous bridges and sections of roads were washed out, power lines downed, with much damage to cars and personal property. Total estimated damages came to $15.5 million. The following are discharge amounts from WEMA Storm Data: Fifteenmile Creek near Worland (May 18) - 4,270 CFS, Big Horn River at Worland (May 19) - 17,500 CFS, Nowood River near Ten Sleep (May 19) - 3,380 CFS, Shoshone River near Lovell (May 18) - 7,680 CFS), Elk Creek near Basin (May 19) - 2,450 CFS, Shell Creek near Greybull (May 19) - 2,150 CFS, Big Horn River near Kane (May 20) - 20,700 CFS, Little Powder River below Corral Creek near Weston (May 18) - 2,410 CFS, Little Powder River above Dry Creek near Weston (May 19) - 4,460 CFS, Little Powder River above Dry Creek near Weston (May 19) - 5,300 CFS, Salt Creek near Sussex (May 18) - 10,200 CFS, Dead Horse Creek near Buffalo (May 18) - 1,420 CFS, Clear Creek below Rock Creek 162? CFS, Powder River near Kaycee (May 18) - 4,200 CFS, Powder River at Sussex (May 19) - 24,000 CFS, South Fork River near Kaycee (May 20) - 8,200 CFS, Bitter Creek near Garland (May 17) - 552 CFS, Whistle Creek near Garland (May 18) - 2,340 CFS, Shoshone River below Buffalo Bill Reservoir (May 19) - 1,230 CFS, Shoshone River near Garland (May 19) - 4,550 CFS, Goose Creek below Sheridan (May 18) - 5,430 CFS, Prairie Dog Creek near Acme (May 19) - 3,940 CFS, Clear Creek at Ucross 1740 (May 19) - 32,500 CFS, Crazy Woman Creek at Upper Station (May 20) - 2,200 CFS, Little Thunder Creek near Hampshire (May 18) - 3,030 CFS, Black Thunder Creek near Hampshire (May 18) - 5,050 CFS, Turner Creek near Osage (May 18) - 2,480 CFS, Beaver Creek near Newcastle (May 19) - 3,870 CFS. The event was estimated to be a 20- to greater than 100-year flood

Sheridan Clearmont to

Leiter July 29, 1985 0 0 $22,500 $0 $22,500

Very heavy rain from storms caused flooding along Clear Creek from Clearmont to Leiter. Some irrigation equipment was damaged.

Sheridan Sheridan,

Goose Creek February 24,

1986 0 0 $0 $0 $0

A 300-foot ice jam along Goose Creek, near Sheridan, blocked the creek, causing water to spill over the banks and into a mobile home park. Two hundred and fifty people were evacuated from the Woodland Park Village Mobile Homes.

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Crop Damage

Total Damage

Information

Sheridan

May 9, 1995 0 0 $0 $0 $0

A combination of moderate to heavy rain and snow melted from the adjacent Big Horn mountains caused some creeks and streams to over flow their banks. In the town of Big Horn (eight miles south of Sheridan), the Jackson Creek flooded several roads. In Story (16 miles south of Sheridan), the North Piney Creek washed out portions of two roads and closed two other roads due to high water.

Sheridan

June 16, 1995 0 0 $0 $0 $0

A combination of snowmelt from the Big Horn Mountains and some rainfall led to flooding along the east side of the mountains in Sheridan County. The Big Goose Creek, the Little Goose Creek, and Piney Creek all overflowed their banks and produced flooding. The Big Horn reservoir and the Park reservoir overflowed and this added to the volume of water that roared down those creeks. Flooding of roads and a few homes was reported in Story (16 miles south of Sheridan). Big Horn (8 miles south of Sheridan), and in the town of Sheridan. Some evacuations were necessary due to the flooding. Sheridan City Park was under water and some farmland in Sheridan County experienced flooding. No injuries or deaths occurred. Damage estimates were not available.

Sheridan Sheridan Foothills

February 7, 1996 0 0 $25,000 $0 $25,000 Warm temperatures produced flooding in Sheridan County. Some basements were flooded. Some small streams and creeks went over their banks and flooded low lying areas and some streets.

Sheridan Sheridan August 19,1998 0 0 $20,000 $0 $20,000 The Little Goose Creek flooded a small subdivision when a slow moving thunderstorm produced over 1.50 inches of rainfall in 20 minutes. A house basement was reported to have been flooded.

Sheridan Sheridan August 21, 2002 0 0 $0 $0 $0 Business owners reported flooded basements downtown.


May 7, 2005

Early Creek and irrigation ditches flooded near Ranchester, as well as basements flooded in Ranchester


May 8, 2005

Water ran across 5th avenue on the west side of town. Water also filled parking lots

Sheridan Sheridan May 10-12, 2005 0 0 $50,000 $0 $50,000

Heavy rain and warm temperatures with a heavy snow pack on the Big Horn Mountains produced flooding in the City of Sheridan. Storm sewers backed up, some basements were flooded and a couple of dikes were washed out along with two culverts that washed out causing two County roads to be closed.


Crop Damage

Total Damage

Information

Sheridan Sheridan May 11, 2005

Bridge washed out 25ESE Sheridan on County Road 161 west of Ulm; Big Goose Creek flooded out of its banks; massive flooding occurred 5S Sheridan on U.S. Highway 87 between Sheridan and Big Horn.

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Water was up to many homes in this area; Water up to car doors at the 2000 block of Main Street; Long Drive in Sheridan was under four feet of water near the hospital. Numerous cars were stalled in the high water.

Sheridan Sheridan June 6-7, 2007 0 0 $0 $0 $0

A large spring storm associated with a cutoff upper level low, moved across the Northern Rockies on the afternoon of June 6th through the morning of June7th. Thunderstorms developed by early afternoon across northern Wyoming and southern Montana, with heavy rainfall beginning in Sheridan, Wyoming and Carbon County, Montana at 330pm and across much of southern Montana by 6pm. By 9pm Wednesday evening, heavy rainfall became more widespread across southern Montana and continued through the overnight hours. By mid-morning on the 6th, rainfall had ended across the impacted area. Runoff from areas upstream of Rosebud County and the Tongue River Reservoir resulted in flooding downstream of the dam. A park was closed in Ranchester due to standing water. Three inches of rain was reported in the Sheridan gage. Water was running over the roads. Rainfall from the storm was 3.20 inches in 12 hours. Five Mile Creek was flooded along with 3rd Avenue West.

Sheridan Ranchester June 6-7, 2007 0 0 $0 $0 $0 Two inches of rain fell in one hour.

Sheridan North Sheridan County, City of

Sheridan May 20, 2011 0 0 $520,000 $0 $520,000

A Pacific low moved into the four corners region on the 17th

and

migrated northeast into the Dakotas through the 22nd

, bringing a round of heavy precipitation aided by a tap of Gulf of Mexico

moisture. Another system passed to the south on the 23rd

and 24th

, continuing the precipitation across the area. Heavy rains of 3 to 5 inches in the Big Horn Mountains and Foothills caused area streams and creeks to rise and result in localized flooding. Small streams and creeks around Dayton were reported to be flooded. In addition, flooding was reported along the Tongue River and Little Goose Creek and on creeks in the Ranchester area resulting in the closing of some county roads. During the height of the heavy rainfall, Pass Creek Road, far northern Sheridan County near the Montana border, flooded and was eventually washed out. Several culverts were also reported as washed out. FEMA Disaster Assistance funding was received for this flood event ($15,000 for Conner Battlefield State Park).

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Crop Damage

Total Damage

Information

Sheridan Sheridan May 25 -27, 2011 0 0 $0 $0 $0

Heavy rainfall in the foothills of the Big Horn Mountains resulted in high flows and localized flooding on all rivers and streams across Sheridan County. County dispatch reported Soldier Creek was out of its banks and flooding homes in Downer Addition subdivision on the west side of Sheridan.

Sheridan Ranchester31 June 8 - 10, 2011 0 0 $0 $0 $0

Another in a series of very wet storm systems moved across the region bringing with it 1 to 2 inches of rainfall. County officials and spotters reported flooding in the southern end of Ranchester on the Tongue River and Five Mile Creek. Several locations in Ranchester had high water with flooding in low lands and back yards of some homes. In addition, rises on the Tongue River caused the streams and creeks feeding into the river to rise as well.

Sheridan Clearmont February 22-23,

2012 0 0 $0 $0 $0

Periods of steady rain falling onto frozen ground resulted in some minor flooding during the afternoon and early evening hours on the 22nd. Flooding of low lying areas, as well as creeks and streams was reported across Eastern Sheridan County including Buffalo Creek near Leiter. Stream gages on Wild Horse Creek near Arvada showed a steep rise of over 3 feet from noon into the early evening hours. In addition, a few basements and a county road were flooded north of Leiter.

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See Event Photos – Ranchester and Conner Battle Field State Park

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Risk Assessment32

FEMA Flood Risk Report, March 2013

Flood risk analysis, data and narrative descriptions presented are from the FEMA Sheridan County Flood Risk Report that was finalized on March 29, 2013. The FEMA Flood Risk Report for Sheridan County defines flood risk analysis as the process of measuring the potential of loss of life, personal injury, economic losses, and property damage resulting from vulnerability to floods. A thorough flood risk analysis will do the following:

Identify the flooding source and determine the flood hazard occurrence probability.

Provide a complete profile of the flood hazard including historical occurrence and previous impacts.

Inventory assets located in the identified flood hazard area.

Estimate potential future flood losses caused by exposure to the flood hazard area.

Flood Risk Summary for unincorporated areas of Sheridan County, the City of Sheridan, Town of Dayton, Town of Ranchester, and Town of Clearmont

The Sheridan County FEMA Flood Risk analysis identifies the following problems and areas of mitigation interest in Sheridan County:

838 parcels intersect the 0.2% annual chance (500‐year) floodplain boundary in the City of Sheridan.

339 parcels which previously did not intersect the floodplain, are now located within the floodplain (Changes since Last FIRM), including 44 in the City of Sheridan and 295 in unincorporated Sheridan County.

1,338 parcels intersect the 1% annual chance (100‐year) floodplain boundary in unincorporated Sheridan County.

There is a cluster of Public Assistance projects in and around the Town of Dayton.

According to the Hazus‐MH analysis, there could be 2,828 displaced people in the event of a 1% annual chance flood, and 1,693 of those people will need shelter.

At‐Risk Buildings and Critical Facilities There are 1,665 parcels located in the 1% annual chance floodplain in Sheridan County, about half of which are residential. 1,338 of these parcels are in the unincorporated County. There are 1,381 parcels exposed to the 0.2% annual chance floodplain. 838 of these are in the City of Sheridan, 75% of which are residential. According to a Hazus‐MH flood analysis, a countywide 1% annual chance flood event could result in $64,223,000 in building damage and 2,828 displaced persons. There are not any critical facilities (including schools, fire stations, police stations, and hospitals) in the DFIRM flood zones.

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This section was incorporated from the FEMA Flood Risk Report, March 28, 2013

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Flood Risk Analysis33

Flood risk analysis is the process of measuring the potential of loss of life, personal injury, economic losses, and property damage resulting from vulnerability to floods. A thorough flood risk analysis will do the following:

Identify the flooding source and determine the flood hazard occurrence probability.

Provide a complete profile of the flood hazard including historical occurrence and previous impacts.

Inventory assets located in the identified flood hazard area.

Estimate potential future flood losses caused by exposure to the flood hazard area.

Identify areas of mitigation interest.

Different analysis methods are used to understand and quantify flood risk. Flood risk assessments can be performed at the state, watershed, census block, community, or parcel level. Flood risk assessments at the watershed level can include identifying how activities and development in one community can affect areas up and down stream. On the parcel or census block level, flood risk analysis can provide more specific data to individual property owners for taking appropriate mitigation action. The Flood Risk Report and Flood Risk Database contain the following information to help describe and visualize flood risk in Sheridan County:

Floodplain map (FIRM)

Floodplain changes since last FIRM

Exposure of buildings and critical facilities in flood hazard areas and estimates of potential losses

Participation in and use of FEMA programs including the NFIP and Public Assistance

Location of dams

Floodplain Map Figure 2 below shows the project area, incorporated communities, and the 1% annual chance flood (100‐year floodplain) and 0.2% annual chance flood (500‐year floodplain) boundaries as delineated on the updated FIRM.

33

FEMA Flood Risk Report, March 28, 2013 Section 2.0: Flood Risk Analysis

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Figure 2: Sheridan County Flood Map Area

Floodplain Changes since Last FIRM

The “Changes Since Last FIRM” dataset identifies changes to Sheridan County’s floodplain boundaries since the last FIRM was created and published. This dataset is created in GIS by digitizing areas that were previously mapped on paper FIRMs and comparing that to the updated digital FIRM data. Figure 4 shows floodplain increases in green and floodplain decreases in orange. There are three additional restudied reaches in southeast Sheridan County that are not represented here. Paper FIRMs were not available for these reaches and therefore the changes since the last FIRM cannot be determined. This information is also noted in the GIS metadata in the Flood Risk Database. Locations of these reaches are the following:

Powder River, extends approximately 2 miles upstream to approximately 2 miles downstream of the Town of Arvada.

Clear Creek, extends approximately 2 miles upstream to 2 miles downstream of the Town of Leiter.

Clear Creek, extends approximately 2 miles upstream to 2 miles downstream of the Town of Clearmont.

Table 4 and Figure 4 presents the results of using GIS to analyze the parcels and critical facilities (hospitals, fire stations, police stations and schools) that intersect the changes in the floodplain from the last FIRM. However, a parcel boundary can intersect the change in the floodplain (increase or decrease), even if the structure(s) in the parcel are located outside of the floodplain change. Therefore, a parcel intersecting a floodplain increase does not necessarily mean that a structure is now “in the floodplain” and likewise, a parcel intersecting a floodplain decrease does not necessarily mean that a structure is now “out of the floodplain”. Table 5 presents the new NFIP Flood Hazard Zone Designations that changed in Sheridan County since the last Flood Hazard Boundary and Floodway Map panels where produced.

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Table 4: Critical Facilities and Parcel Changes from the Effective paper FIRMs for participating NFIP

communities to the 2012 DFIRMs

Increased Floodplain Decreased Floodplain

Critical Facilities 0 1 (school)

Parcels

339 parcels intersecting the floodplain, including 44 in the City of Sheridan and 295 in unincorporated

Sheridan County

578 parcels intersecting the floodplain, including 203 in the City of Sheridan, and 375 in unincorporated Sheridan County

Table 5: Updated Flood Hazard Zone Designations for Sheridan County and Incorporated Communities

Old Zone(s) New Zone

A1 through A30 AE

V1 VE

B X

C X

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Figure 4: Central Sheridan County Changes Since Last FIRM

Building Exposure and Loss Estimates GIS was used to intersect the DFIRM with the parcel boundaries to calculate an estimated count of structures exposed to the flood. Table 6 shows the count of parcels intersecting the 1% annual chance floodplain and 0.2% annual chance floodplain by jurisdiction, and the percent of those structures that are residential. Note that if a floodplain intersects a parcel boundary, this does not necessarily mean that the structure in that parcel falls within the floodplain. Instead, it is a conservative estimate of exposure. Parcel boundaries that intersect the floodplain and critical facilities in Sheridan County are shown in the maps in Figures 5-8. Based on the analysis, there are not any police stations, fire stations, hospitals, or schools that intersect DFIRM floodplains.

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Table 6: Number of Parcels Intersecting FIRM Floodplains by Jurisdiction

Jurisdiction 1% Annual Chance 0.2% Annual Chance

Parcel Count % Residential Parcel County % Residential

Clearmont 4 100% 0

Dayton 51 92% 0

Ranchester 91 68% 9 56%

Sheridan 185 70% 838 75%

Unincorporated 1,334 46% 534 57%

Totals 1,665

1,381

A separate analysis was done using Hazus‐MH, FEMA’s loss estimation tool, which combines information about the location and magnitude of the flood with the built environment to estimate losses. Table 7 shows Hazus‐generated damaged building counts, economic losses, displaced population and population needing shelter. These loss estimates were calculated for the 1% annual chance flood event in the populated areas of Sheridan County. The model used a 10‐meter digital terrain model and depth to damage relationships to estimate losses to buildings and impacts to the population. Default Hazus‐ MH data (buildings and population) is linked to census block geography and assumes that there is an even distribution of buildings and population across a census block. Hazus‐MH default floodplain modeling and low‐resolution inventory data may contribute to inaccuracies in the results.

Table 7: Sheridan County Hazus‐MH Loss Estimates

Total Damaged Building County

Total Building Economic Loss

Displaced Population

Shelter Needs

229 $65,223,000 2,828 1,693

The Sheridan County Flood Risk Database includes the following:

FIRM 1% annual chance and 0.2% annual chance floodplain boundaries

Parcel layer with intersecting flood zone designation as an attribute

Hazus‐MH 1% annual flood estimates of total direct economic losses for buildings, including direct building losses, contents losses, and income‐related losses, and estimates of displaced population and shelter needs

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Figure 5: City of Sheridan Parcels Intersecting FIRM Floodplains

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Figure 6: Town of Dayton Parcels Intersecting FIRM Floodplains

74

Figure 7: Town of Ranchester Parcels Intersecting FIRM Floodplains

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Figure 8: Town of Clearmont Parcels Intersecting FIRM Floodplains

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Ice Jamming Overview34 Ice forms in freshwater bodies whenever the surface water cools to 0 degrees Celsius (32 degrees Fahrenheit) or less. USACE reports the following forms of ice. Sheet ice forms in calm water, such as lakes or reservoirs, or in slow-moving river reaches, where the flow velocity is less than 0.5 m/s (1.5 ft/s).

Types of Ice Jams An ice jam is a stationary accumulation of ice that restricts water flow. Ice jams cause substantial increases in upstream water levels, while downstream water levels may drop. USACE reports the following types of ice jams. Freeze-up jams. Freeze-up jams are composed primarily of frazil ice, with some fragmented ice included, and occur during early winter to midwinter.

Breakup jams. Breakup jams occur during periods of thaw, generally in late winter and early spring, and are composed primarily of fragmented ice formed by the breakup of an ice cover or freeze-up jam.

Combination jams. Combination jams involve both freeze-up and breakup jams. For example, a small freeze-up jam forms in a location that causes no immediate damage.

Frazil ice consists of small particles of ice formed in highly turbulent, super cooled water, such as river rapids or riffles, during cold, clear winter nights when the heat loss from the water to the atmosphere is very high.

Fragmented ice is made up of ice pieces that originated as consolidated frazil ice pans or from the breakup of sheet ice growing at the surface of slow-moving water.

Brash ice is an accumulation of ice pieces less than 1.5 to 2 m (5 to 6 ft) in maximum dimension resulting from the breakup of an ice cover by increasing water flow or by vessel passage.

Causes of Ice Jams

The USACE attributes the following as primary causes of ice jams:

River geometries, weather characteristics, and floodplain land-use practices contribute to the ice jam flooding threat at a particular location.

Obstructions to ice movement can cause ice jams, for example closely spaced bridge or dam piers. In high runoff situations, a partially submerged bridge superstructure obstructs ice movement and may initiate a jam. In smaller rivers trees along the bank sometimes fall across the river causing an ice jam.

Some structural or operational changes in reservoir regulation may lead to ice jams.

34

State of Wyoming Multi-Hazard Mitigation Plan, Chapter 8 Flood (http://wyohomelandsecurity.state.wy.us/mitigation_plan.aspx)

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Ice Jam Flood Losses

The U.S. Army Corps of Engineers (USACE) details the following losses as attributable to ice jam flooding in Sheridan County. Ice jam flooding is responsible for loss of life, although the number of fatalities in the United States is considerably less than non-ice jam flooding. Ice jams in the United States cause approximately $125 million in damages annually, including an estimated $50 million in personal property damage and $25 million in operation and maintenance costs to USACE navigation, flood control, and channel stabilization structures.

City of Sheridan Ice Jam, Sheridan County 2009. Estimated cost of ice breakup effort to restore proper channel flow, $15,000.

History The following records list the reported ice jams for Sheridan County from 1922 through 2009. The recorded ice jams are listed chronologically. The data were provided by the Ice Engineering Group with the U.S. Army Corps of Engineers - Cold Regions Research and Engineering Laboratory (CRREL) and have been reported by Hydrologic Unit Codes (HUCs).

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Table 8: Reported Ice Jams for Sheridan County 1922-1971

Date County City River

3/16/1922 Sheridan Arvada Powder River





3/25/1943 Sheridan Arvada Clear Creek














1/9/1959 Sheridan Ucross Piney Creek




3/19/1960 Sheridan Sheridan Goose Creek

3/19/1960 Sheridan Ucross Piney Creek


1/1/1971 Sheridan Parkman West Fork Little Bighorn River

2/16/1971 Sheridan Acme Prairie Dog Creek

2/25/1986 Sheridan Acme Goose Creek

2/6/1996 Sheridan Dayton East Pass Creek

11/28/2003 Sheridan Dayton East Pass Creek

1/8/2004 Sheridan Parkman West Pass Creek

2/22/2004 Sheridan Acme Prairie Dog Creek

2/22/2004 Sheridan Acme Goose Creek

2/26/2004 Sheridan Sussex Powder River


2/25/2009 Sheridan Sussex Powder River


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Flood Mitigation Strategy35

Mitigation helps to reduce or eliminate the impacts of hazard events and provides a critical foundation for creating safer, more disaster resilient communities. As a community better understands its flood risk, it can identify mitigation actions to reduce future losses and protect people and property.

Mitigation Success in Sheridan County

Flood mitigation actions are powerful tools to communicate the concepts of mitigation and result in more resilient communities. Both structural and non‐structural measures have been implemented in thousands of communities and have the following benefits:

Demonstrate losses reduced or avoided

Educate citizens and officials on available flood hazard mitigation techniques Sheridan County can celebrate several mitigation successes over the past decade. The Sheridan County Multi‐Hazard Mitigation Plan was approved in 2009. The plan identifies a number of County and City actions to reduce future flood losses. Mitigation actions that were identified as ongoing flood projects in that Plan include the following: Little Goose Creek Levee Channel Widening Project, Tongue River, Clear Creek, Piney Creek, Powder River Flood Control Projects. An addition mitigation success was the completion of the National Oceanic and Atmospheric Administration (NOAA) National Weather Service Stream Gages and Early Warning Systems. A number of projects were listed in the plan as being completed by 2009, including: Linden, Huntington, South Downtown, West Downtown, North Gould, North Broadway, and Sumner Street Storm Sewer Projects, Dana Avenue Roadway Repair Project, 11th Street Bridge Undermining Project, Junior High Hill LaClede Sanitary Sewer Project, North Main/Higby Road and Champion Drive Drainage Projects, Sanitary Sewer Creek Crossings at Goose Creeks. The completion of the Army Corp of Engineers (USACE) Section 22 hydrologic and hydraulic analysis of Big Goose Creek, Little Goose, Goose, and Soldier Creek within the City of Sheridan and unincorporated areas of Sheridan County was an additional success for the City of Sheridan and Sheridan County. The USACE section 22 study was completed in December 2010 and the data and mapping products where incorporated into the 2014 FEMA Flood Insurance Study (FIS)36 and new Flood Hazard Maps for the City of Sheridan and unincorporated areas of Sheridan County. Other flood mitigation projects include:

The South Park Floodplain preservation project. The City of Sheridan purchased 38.5 acres of undeveloped floodplain to preserve and create a natural park. The City of Sheridan estimated the South Park Floodplain preservation purchase to cost $450,000.

The Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS) serves as a large pool of observers who have real-time reporting capabilities to get the word out about hazardous conditions. This network is active in Sheridan County and contributes to the efforts of the National Weather Service’s current weather conditions and warnings, forecasting and weather

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FEMA Flood Risk Report, March 28, 2013 Section 3.0 Mitigation 36

Preliminary FEMA Flood Insurance Study, May 22, 2012. Final FIS will be available January 2014.

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data history by submitting Significant Weather reports as an event is occurring. There have been many cases where warnings have been issued based upon those reports37.

National Oceanic and Atmospheric Administration (NOAA) National Weather Service Stream Gages and Early Flood Warning Systems A local flood warning system is defined as a community or locally based system consisting of volunteers, rainfall, river and other hydrologic gages, hydrologic models or procedures, a communications network and a community flood coordinator responsible for issuing a flood warning. Local flood warning systems are classified as manual or automated. Currently Sheridan County has six precipitation gages and seven stream gages that are part of the Sheridan County Early Flood Warning System38.

Table 9: Sheridan County Early Flood Warning System Stations

Station Name Precipitation Gage Stream Gage

Goose Creek X X

Big Goose Creek X X

Big Goose Creek at Canyon

X

West Fork Big Goose Creek

X

Beaver Creek X

Little Goose X X

Little Goose in Canyon

X

Rapid Creek X

Twin Lakes Reservoir X

East Fork Big Goose

X

37

Water Resources Data System – Wyoming State Climate Office 38

NOAA Stream and Precipitation Gage website - http://water.weather.gov/ahps/

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Figure 9: Map of Sheridan County Early Flood Warning System Stations

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Hazard Mitigation Assistance Projects

The Hazard Mitigation Assistance grant programs provide funding for eligible mitigation activities that reduce disaster losses and protect life and property from future disaster damage. At the time of this plan update Sheridan County was awarded two Federal Emergency Management Agency (FEMA) Hazard Mitigation Assistance (HMA) projects totaling more than $255,00039. Sheridan County submitted the HMA grant applications in 2012 following Wyoming's 2011 flooding disaster and is currently funded under the Hazard Mitigation Grant Program (HMGP) through 2015 to complete the proposed bank stabilization projects.

Sheridan County HMGP HMA Projects

Kooi Road Project: $157,355 total funding: $118,016 Federal; $39,339 Local Match. Intent: Protect County Road 93 & a newly-constructed bridge which provide the only public access to residences south of Tongue River. Grant award agreement fully executed 3/12/2013. Period of Performance is 1/28/2013 thru 7/31/2015.

Tongue River Project: $99,563 total funding: $74,672 Federal; $24,891 Local Match. Intent: Protect County Road 92 (Tongue Canyon Road) which provides the only public access to residences & recreational opportunities in Tongue River Canyon & is the primary access to Dayton's Water Treatment Plant. Grant Award Agreement fully executed 4/11/2013. Period of Performance: 5/5/2013 thru 7/31/2015.

Types of Mitigation Actions Flood mitigation actions generally fall into the following four categories: Local Plans and Regulations These actions include government authorities, policies, or codes that influence the way land and buildings are developed and built. Structure and Infrastructure Projects These actions involve modifying existing structures and infrastructure to protect them from a hazard or remove them from a hazard area. This could apply to public or private structures as well as critical facilities and infrastructure. This type of action also involves projects to construct manmade structures to reduce the impact of hazards. Examples include:

Acquisitions and elevations of structures in flood prone areas

Utility undergrounding

Structural retrofits

Floodwalls and retaining walls

Detention and retention structures

Culverts

39

HMGP project data provided by the Wyoming Office of Homeland Security

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Safe rooms

Natural Systems Protection These are actions that minimize damage and losses and also preserve or restore the functions of natural systems. Examples include:

Sediment and erosion control

Stream corridor restoration

Forest management

Conservation easements

Wetland restoration and preservation

Education and Awareness Programs These are actions to inform and educate citizens, elected officials, and property owners about hazards and potential ways to mitigate them. Although this type of mitigation reduces risk less directly than structural projects or regulation, it is an important foundation. Examples include:

Radio or television spots

Websites with maps and information

Real estate disclosure

Presentations to school groups or neighborhood organizations

Mailings to residents in hazard‐prone areas

StormReady , http://www.stormready.noaa.gov/ Emergency Protective Measures Although not considered a mitigation technique, emergency service measures can minimize the impacts of flooding on people and property. Actions commonly taken immediately prior to, during, or in response to a hazard event include:

Hazard warning system

Emergency response plan

Continuity of Operations (COOP) or Continuity of Governance (COG) planning

Critical facilities protection

Health and safety maintenance

Post flood recovery planning

Proposed Sheridan County Mitigation Projects for Flooding and Ice Jamming

Champion Drive Drainage Project

Little Goose Creek (Levee, widening channel)

Tongue River

Piney Creek

Powder River

Clear Creek

Enforcement of floodplain management requirements under the National Flood Insurance

Program

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Updated Project List for 2014-2019 Sheridan County Multi-Hazard Mitigation Plan

Replace Louis Street Bridge

Illinois Neighborhood Reconstruction

North Sheridan Interchange

Loucks Street and Utility Project

Colony South Water Line Replacement

West Downtown Phase IV

Wyoming Park Phase III

Big Goose Creek Sewer Upsize

East Downtown Phase I

Flood Mitigation Programs and Assistance

Not all mitigation activities require funding (e.g., local policy actions such as strengthening a flood damage prevention ordinance), and those that do are not limited to outside funding sources (e.g., inclusion in local capital improvements plan, etc.). For those mitigation actions that require assistance through funding or technical expertise, several state and federal agencies have hazard mitigation grant programs and offer technical assistance. These programs may be funded at different levels over time or may be activated under special circumstances such as after a presidential disaster declaration.

Summary of Flood and Ice Jamming Impact

Property Affected: High Population Affected: Medium Probability: Medium Jurisdictions Affected: City of Sheridan, Town of Dayton, Town of Ranchester, and portions of the unincorporated county

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Hail

Summary of Hail Section Update

• Expansion of Hail History Table to include events from 1937-2013. There was a significant data gap in the 2009 Hail History table that has been corrected and expanded upon.

• New Mitigation Actions section which indicates appropriate Hail mitigation measures.

Hail

Hail causes more than a billion dollars of property damage nationally each year, mostly to crops. The

southeast corner of Wyoming lies within the nations “Hail Alley”. Together with adjacent portions of

Colorado and Nebraska, this region of Wyoming is battered by more hailstorms than any other part of

the United States. Climatological data shows this area of Wyoming averaging five to nine days annually

when hail is reported. While Sheridan County is not in “Hail Alley”, damaging hail storm have still

occurred.

History

There have been 16 damaging hail storms in Sheridan since 1961, which equates to a damaging hail

storm every 2.7 years. Highlights from the history are below. Table 1 presents a complete history of

damaging hail storms. The data were derived from the monthly Storm Data reports generated and

released by the National Oceanic and Atmospheric Administration’s National Climate Center. Other

sources are unpublished reports from the Wyoming Office of Homeland Security, newspaper accounts,

and periodicals from public libraries. The table represents hail storms that have caused damage, injuries,

or loss of life. One of the most damaging events occurred on July 25, 1979, causing more than

$2,750,000 in damage. Documented damaging hail events have occurred in May, June, and July.

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Table 1: Sheridan County Hail Event History 1937-2013

Start /End Date County Location

Estimated

Property

Damage

Estimated Crop

Damage Information

6/17/1937 Sheridan Dome Lake

Hail storms were numerous in all parts of the state. The damage was considerable

in Campbell, Converse, Hot Springs, Johnson, Lincoln, Sheridan, Sublette,

Sweetwater, Washakie, and Weston Counties. Large numbers of lambs, calves, and

fowls were killed and crops ruined.

5/1/1938 Sheridan

Some damage from hail in the lower Big Horn Basin and portions of Sheridan,

Platte, Goshen and Laramie Counties. However, in most places the hail was small

and with only slight damage to vegetation.

10/3/1940 Sheridan Clearmont 1,500 10,000

A damaging hail storm occurred near Clearmont on the afternoon of October 3rd.

Damage to crops was estimated at about $10,000 and buildings at about $1500.

Due to the storm striking late in the season, the principal crop damage was to beets

and alfalfa.

7/12/1943 Sheridan Sheridan

A damaging storm occurred at the Sheridan Field Station on the same date.


On the afternoon of the 9th, a hailstorm in the vicinity of the Sheridan Field Station

did considerable damage to growing crops.

6/18/1951 Sheridan

Northeast

portion of the

state

40,000

A series of hail storms over the northeast portion of the State on the 18th caused

about $40,000 damage. While some damage occurred to growing crops, the

principal damage was to buildings and automobiles.

7/16/1954 Sheridan Clearmont

Hail caused considerable damage near Clearmont and Carpenter on the 16th

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Estimated

Property

Damage

Estimated Crop

Damage Information

9/4/1954 Sheridan Clearmont 5

SW

An intense hailstorm at Clearmont 5 SW, during the evening of the 4th, caused

flood damage of about $1000 to reservoirs and irrigation ditches.

7/6/1956 Sheridan

Moderate losses were reported from hail in Sheridan County on July 6.

8/27/1956 Sheridan

During the afternoon of the 27th a hail and windstorm moved northeastward over

Johnson and southern Sheridan Counties causing crop damage along a 50-mile path

down the Powder River Valley. Most damage was in the vicinity of Clearmont.

Sheridan Weather Bureau Airport station reported some hail about three-fourths

inch in diameter, but distribution was spotty with little damage. Local hail storms

with less damage occurred in many areas.


On the 28th, a thunderstorm with some hail at Clearmont 5 SW caused

considerable damage to crops and irrigation ditches.

6/2/1957 Sheridan Arvada

In the vicinity of Arvada the evening of the 2nd hail broke windows, damaged roofs,

and extensively damaged growing wheat.


On the 6th more hail fell. Crops suffered appreciable damage.

5/20/1961 Sheridan Dayton 2,750 2,750 Thunderstorms with hail, mostly under 1 inch in diameter but some from 1.5 to 2

inches.

6/12/1962 Sheridan Sheridan 8 W

275 Hail measuring 1 to 1.5 inches caused some damage to range land.

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Estimated

Property

Damage

Estimated Crop

Damage Information

7/5/1962 Sheridan Banner

27,500 Heavy rains and several inches of hail caused flash flooding and hail damage to

crops in the Banner vicinity.

7/9/1962 Sheridan Big Horn

27,500 Heavy rains and several inches of hail caused flash flooding and hail damage to

crops in the Big Horn vicinity.

7/27/1965 Sheridan

2,750

Heavy rains and some 1.5-inch-diameter hail caused considerable damage to crops

and property east and southeast of Sheridan. Hardest hit were the Cat and Clear

Creek areas.

8/5/1966 Sheridan Sheridan 25

NW

275 Hail 0.75-inch diameter fell, small damage to range.

6/5/1976 Sheridan Sheridan 25

NE 2,750 Hail 1.75-inch diameter fell over open range.

7/5/1976 Sheridan Leiter 27,500

Hail up to 1.75 inches did damage to buildings, gardens, crops, etc. in and west of

Leiter.

6/16/1977 Sheridan Sheridan 27,500

Hail 1 to 2-inch diameter did damage to houses, cars, crops, etc., and lightning

killed one horse.

8/6/1977 Sheridan

275,000

Hail up to 0.75 inch fell intermittently from just west of Sheridan 0.5 to 1 mile wide

for 20 miles to the east. Most damage was to crops with some cars and buildings.

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Estimated

Property

Damage

Estimated Crop

Damage Information

7/25/1979 Sheridan

2,750,000

"Extensive" damage to several school buildings, homes, and vehicles occurred when

a severe evening thunderstorm dumped golf ball- to baseball-sized hail over parts

of the city and nearby wheat fields.

8/1/1979 Sheridan

275,000

A late afternoon hailstorm hit the Sheridan area causing damage to school

buildings, homes, and vehicles. Size of hail was not reported.

6/6/1981 Sheridan

275,000

A thunderstorm dropped golf ball-sized hail for 15 minutes in the town of Dayton.

Between 75 and 100 homes received damage as well as trees and vehicles.

6/13/1984 Sheridan Northeast

Wyoming

Strong thunderstorms scattered throughout northeast Wyoming produced

widespread minor damage to ranch outbuildings and mobile homes as marble-sized

hail and winds up to 50 MPH struck the area. Some hail as large as golf balls fell

near Ranchester, 20 miles northwest of Sheridan. Winds were also reported to be

near 60 MPH in the Upton and Sundance areas.

5/4/1993 Sheridan

27,500

Hail up to an inch was recorded at the airport as well as the Law Enforcement

Center in town. Damage was slight with no injuries.


Hail 1.75 inches in magnitude

5/13/1996 Sheridan Leiter

Hail 1 inch and 1.25 inches in magnitude

6/14/1996 Sheridan Parkman,

Sheridan

Hail .75 inch magnitude

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Estimated

Property

Damage

Estimated Crop

Damage Information






Hail .81 and .88 inch magnitude




Hail 1.75 inch magnitude. Golf ball sized hail was reported between Sheridan and

Ucross




Hail .88 inch magnitude. Spotter report of nickel size hail.


Hail .88 inch magnitude. Several reports of nickel and dime size hail near Sheridan.

6/24/2000 Sheridan Ranchester

Hail 1.25 inch magnitude

6/3/2001 Sheridan Sheridan,

Clearmont

Hail .75 - 1.0inch magnitude. Wind damage. 3.5 foot diameter tree blown down

near Ucross. 1.00 inch hail drifted and was still present on the morning of the 4th.

6/27/2001 Sheridan Leiter,

Clearmont Hail 1.0 inch magnitude



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Estimated

Property

Damage

Estimated Crop

Damage Information

7/14/2001 Sheridan 5 NE Sheridan

Hail 1.75 inch magnitude. Windshield broken and vehicle damaged. Minor flooding

over roads. Hail floating on water




Hail 1.75 inch magnitude. Hail drifted over a foot deep

7/26/2001 Sheridan

Sheridan,

Ranchester,

Clearmont,

Dayton


6/8/2002 Sheridan Ucross


8/21/2002 Sheridan

Sheridan,

Ranchester,

Clearmont,

WYARNO

Hail .75 - .88 inch magnitude. Ground whitened by hail. Report also of 2.35 inches

of rain. 1.50 inches of rain in 45 minutes. Some street flooding briefly occurred but

receded quickly.





6/10/2004 Sheridan Dayton


6/20/2004 Sheridan Ranchester,

Sheridan

Ranchester - 1.74 inch magnitude. Sheridan - 1.00 inch magnitude, hail on north

side of town.

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Estimated

Property

Damage

Estimated Crop

Damage Information








Hail 1.0 inch magnitude. Hail broke windows at spotters' home


Hail .75, .88, and 1.0 inch magnitude. Funnel cloud also reported by law

enforcement on Interstate 90. Crops were flattened and vehicles were dented.


Hail 1.25 inch magnitude. A severe thunderstorm rapidly developed just west of

Sheridan and moved over the city during the early evening hours of the 7th.

Numerous street flooding along with downed power lines and tree limbs were

reported. Numerous power outages were reported in the city of Sheridan due to

70 mph wind gusts.

6/2/2008 Sheridan Kendrick,

Clearmont

Hail .75 - 1.75 inch magnitude. Severe thunderstorms resulting in large hail moved

across Sheridan County in the Billings County Warning area. This was the first

severe weather outbreak for the area. Storm damage reports consisted of vehicle

damage, skylight broken, and screens ripped.

6/18/2008 Sheridan Ranchester

Severe thunderstorms producing large hail moved across Sheridan County during

the late afternoon and evening hours of the 18th.

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Estimated

Property

Damage

Estimated Crop

Damage Information

6/19/2008 Sheridan Dayton,

Sheridan

Hail .75, .88, 1.0, and 1.5 inch magnitude. Severe thunderstorms producing large

hail moved across Sheridan County during the late afternoon and early evening

hours of the 19th. Quarter size hail was reported at I-90 and Main Street on the

north side of Sheridan. Ping pong ball size hail was reported on the south side of

Sheridan at Sheridan College.

6/22/2008 Sheridan

Ranchester,

Sheridan,

ACME

Hail .75, .88, and 1.75 inch magnitude. A severe thunderstorm producing strong

winds and hail moved across Ranchester and Sheridan, Wyoming during the

evening of the 22nd. Sheridan reported a wind gust of 60 mph.

6/25/2008 Sheridan Big Horn,

Clearmont

Hail .88 inch magnitude. A severe thunderstorm producing hail moved across

Sheridan County.

7/6/2008 Sheridan Story,

Banner, Ulm

Hail .75 and 1.0 inch magnitude. Severe thunderstorms producing large hail,

moved across Sheridan County Wyoming during the early afternoon hours of the

6th.

7/17/2008 Sheridan Arvada

Hail .75 and .88 inch magnitude. A severe thunderstorm producing severe hail

moved across Sheridan County on the evening of the 17th.

7/18/2008 Sheridan Big Horn,

Banner, Ulm

Hail .88 and 1.50 inch magnitude. Severe thunderstorms producing large hail

moved across Sheridan County during the early evening hours of the 18th.


Hail .75 and .88 inch magnitude. A few thunderstorms moved across Sheridan

County from the 17th through the 21st. However, given the new hail criteria, these

were not severe.

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Estimated

Property

Damage

Estimated Crop

Damage Information


Hail .75 and .88 inch magnitude. A few thunderstorms moved across Sheridan

County from the 17th through the 21st. However, given the new hail criteria, these

were not severe.

7/13/2009 Sheridan WYARNO

Hail 1.0 inch magnitude. Severe thunderstorms moved across portions of Northern

Wyoming in the Billings County Warning Area during the afternoon hours of the

13th.

7/15/2009 Sheridan Banner

Hail .75 inch magnitude. A thunderstorm producing 3/4 hail moved just southeast

of Sheridan. The hail lasted five minutes.

8/4/2009 Sheridan

Dayton,

Ranchester,

Ft.

Mackenzie,

ACME

Hail 1.0 inch magnitude. Severe thunderstorms producing strong winds and large

hail moved across Northern Wyoming during the afternoon of the 4th.

8/7/2009 Sheridan Dayton

Hail 1.0 inch magnitude. The largest severe weather outbreak of the summer

occurred during the afternoon and evening hours of the 7th. A moist and very

unstable atmosphere was in place across South Central and Southeast Montana, as

well as Northern Wyoming. An upper level disturbance combined with a cool front

moving across the Billings County Warning Area allowed for the development of

severe thunderstorms producing high winds and large hail. Very heavy rain also

accompanied the thunderstorms. The bulk of the severe weather occurred across

Southern and Southeast Montana.

91


Estimated

Property

Damage

Estimated Crop

Damage Information

6/20/2010 Sheridan

Story,

Ranchester,

Kleenburn

Hail 1.0 - 2.75 inch magnitude. Meteorologically speaking, this was a very active

severe weather day for south central Montana and Northern Wyoming. A very

moist and unstable atmosphere was in place across portions of the Billings Forecast

area during the afternoon and evening of the 20th (Father's Day). A moist,

southeast surface flow, strong wind shear aloft, and ample afternoon heating

provided the necessary ingredients for severe weather. Numerous thunderstorms,

some of which became rapidly severe producing large hail, developed across North

Central Wyoming.

6/30/2010 Sheridan Ranchester,

Kleenburn

Hail .75 and 1.0 inch magnitude. A severe thunderstorm produced large hail in the

Sheridan area.


Hail .75 inch magnitude. An isolated thunderstorm producing sub-severe hail

moved across portions of Sheridan County.

6/30/2011 Sheridan Banner, Leiter

Hail 1.0 and 1.25 inch magnitude. A couple of thunderstorms producing large hail

and damaging winds moved across Sheridan County Wyoming, as well as Carter

County in southeast Montana. Extensive 1/4 to 1/2 hail was also reported. In

addition to the hail, 0.70 inches of rain was reported.

7/11/2011 Sheridan Kleenburn

Hail 1.0 inch magnitude. An isolated thunderstorm over Sheridan County produced

large hail and strong winds. Estimated winds of 65-70 mph resulting in 3-4 inch

Cottonwood tree limbs breaking off were also reported.

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Estimated

Property

Damage

Estimated Crop

Damage Information

5/26/2013 Sheridan

Story,

Banner, Big

Horn,

Wakeley

Hail 1.0 - 2.50 inch magnitude. Moderate instability and sufficient vertical shear

resulted in the development of severe thunderstorms across portions of the Billings

Forecast Area during the afternoon and evening hours of the 26th.


Hail 1.0 inch magnitude. A thunderstorm that moved across the Sheridan Foothills

produced some large hail and damaging winds. Numerous reports of hail ranging

in size from pea to quarter were received in and around the Sheridan area.

6/13/2013 Sheridan Sheridan Large hail event. Hail 1.75 inch magnitude.

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Impacts

Hail storms have occurred in every county in Wyoming, although hail damage has only occurred in

twenty-two counties. Sublette and Uinta counties have no recorded hail damage. Figure below shows

the distribution of the number of hail storms, number of deaths and injuries, and amount of crop and

property damage in reported dollars. The total documented hail damage for Sheridan County is

$3,051,250 in year of damage dollars and $7,175,625 in 2004 dollars.

Hail Damages by County

Potential Future Damage Impacts Sheridan County is in a hail prone region of Wyoming and will continue to experience damaging events

during the summer months, based on a recurrence interval of every 2.7 years. Based on the past

documented storm damage (1979) converted to 2004 dollars it is suggested that $7.1 million, at a

minimum, be used as the potential cost of the worst-case future hail storm in Sheridan County. Future

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hail storms will impact private and public property such as cars, roofs, equipment, buildings and

agricultural crops and livestock.

Proposed Sheridan County Mitigation Projects for Hail

Encourage residents, businesses and schools to purchase NOAA weather radios.

Weather Spotter Training for Sheridan County residents

Summary PROPERTY AFFECTED: Medium POPULATION AFFECTED: Medium PROBABILITY: Medium JURISDICTION AFFECTED: County

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